[PATCH] vhost: Add polling mode
Hello All,
When vhost is waiting for buffers from the guest driver (e.g., more
packets
to send in vhost-net's transmit queue), it normally goes to sleep and
waits
for the guest to "kick" it. This kick involves a PIO in the guest, and
therefore an exit (and possibly userspace involvement in translating this
PIO
exit into a file descriptor event), all of which hurts performance.
If the system is under-utilized (has cpu time to spare), vhost can
continuously poll the virtqueues for new buffers, and avoid asking
the guest to kick us.
This patch adds an optional polling mode to vhost, that can be enabled
via a kernel module parameter, "poll_start_rate".
When polling is active for a virtqueue, the guest is asked to
disable notification (kicks), and the worker thread continuously checks
for
new buffers. When it does discover new buffers, it simulates a "kick" by
invoking the underlying backend driver (such as vhost-net), which thinks
it
got a real kick from the guest, and acts accordingly. If the underlying
driver asks not to be kicked, we disable polling on this virtqueue.
We start polling on a virtqueue when we notice it has
work to do. Polling on this virtqueue is later disabled after 3 seconds of
polling turning up no new work, as in this case we are better off
returning
to the exit-based notification mechanism. The default timeout of 3 seconds
can be changed with the "poll_stop_idle" kernel module parameter.
This polling approach makes lot of sense for new HW with posted-interrupts
for which we have exitless host-to-guest notifications. But even with
support
for posted interrupts, guest-to-host communication still causes exits.
Polling adds the missing part.
When systems are overloaded, there won?t be enough cpu time for the
various
vhost threads to poll their guests' devices. For these scenarios, we plan
to add support for vhost threads that can be shared by multiple devices,
even of multiple vms.
Our ultimate goal is to implement the I/O acceleration features described
in:
KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon)
https://www.youtube.com/watch?v=9EyweibHfEs
and
https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html
Comments are welcome,
Thank you,
Razya
From: Razya Ladelsky
Add an optional polling mode to continuously poll the virtqueues
for new buffers, and avoid asking the guest to kick us.
Signed-off-by: Razya Ladelsky
---
drivers/vhost/net.c |6 +-
drivers/vhost/scsi.c |5 +-
drivers/vhost/vhost.c | 247
+++--
drivers/vhost/vhost.h | 37 +++-
4 files changed, 277 insertions(+), 18 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 971a760..558aecb 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -742,8 +742,10 @@ static int vhost_net_open(struct inode *inode, struct
file *f)
}
vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX);
- vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT,
dev);
- vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN,
dev);
+ vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT,
+ vqs[VHOST_NET_VQ_TX]);
+ vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN,
+ vqs[VHOST_NET_VQ_RX]);
f->private_data = n;
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 4f4ffa4..56f0233 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1528,9 +1528,8 @@ static int vhost_scsi_open(struct inode *inode,
struct file *f)
if (!vqs)
goto err_vqs;
- vhost_work_init(&vs->vs_completion_work,
vhost_scsi_complete_cmd_work);
- vhost_work_init(&vs->vs_event_work, tcm_vhost_evt_work);
-
+ vhost_work_init(&vs->vs_completion_work, NULL,
vhost_scsi_complete_cmd_work);
+ vhost_work_init(&vs->vs_event_work, NULL, tcm_vhost_evt_work);
vs->vs_events_nr = 0;
vs->vs_events_missed = false;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c90f437..678d766 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -24,9 +24,17 @@
#include
#include
#include
+#include
#include
#include "vhost.h"
+static int poll_start_rate = 0;
+module_param(poll_start_rate, int, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(poll_start_rate, "Start continuous polling of virtqueue
when rate of events is at least this number per jiffy. If 0, never start
polling.");
+
+static int poll_stop_idle = 3*HZ; /* 3 seconds */
+module_param(poll_stop_idle, int, S_IRUGO|S_IWUSR);
+MODULE_PARM_DESC(poll_stop_idle, "Stop continuous polling of virtqueue
after this many jiffies of no work.");
enum {
VHOST_MEMORY_MAX_NREGIONS = 64,
@@ -58,27 +66,27 @@ static int vhost_poll_wakeup(wait_queue_t *wait,
unsigned mode, int sync,
return 0;
}
-void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
+void v
[PATCH] vhost: Add polling mode
From: Razya Ladelsky Date: Thu, 31 Jul 2014 09:47:20 +0300 Subject: [PATCH] vhost: Add polling mode When vhost is waiting for buffers from the guest driver (e.g., more packets to send in vhost-net's transmit queue), it normally goes to sleep and waits for the guest to "kick" it. This kick involves a PIO in the guest, and therefore an exit (and possibly userspace involvement in translating this PIO exit into a file descriptor event), all of which hurts performance. If the system is under-utilized (has cpu time to spare), vhost can continuously poll the virtqueues for new buffers, and avoid asking the guest to kick us. This patch adds an optional polling mode to vhost, that can be enabled via a kernel module parameter, "poll_start_rate". When polling is active for a virtqueue, the guest is asked to disable notification (kicks), and the worker thread continuously checks for new buffers. When it does discover new buffers, it simulates a "kick" by invoking the underlying backend driver (such as vhost-net), which thinks it got a real kick from the guest, and acts accordingly. If the underlying driver asks not to be kicked, we disable polling on this virtqueue. We start polling on a virtqueue when we notice it has work to do. Polling on this virtqueue is later disabled after 3 seconds of polling turning up no new work, as in this case we are better off returning to the exit-based notification mechanism. The default timeout of 3 seconds can be changed with the "poll_stop_idle" kernel module parameter. This polling approach makes lot of sense for new HW with posted-interrupts for which we have exitless host-to-guest notifications. But even with support for posted interrupts, guest-to-host communication still causes exits. Polling adds the missing part. When systems are overloaded, there won't be enough cpu time for the various vhost threads to poll their guests' devices. For these scenarios, we plan to add support for vhost threads that can be shared by multiple devices, even of multiple vms. Our ultimate goal is to implement the I/O acceleration features described in: KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) https://www.youtube.com/watch?v=9EyweibHfEs and https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html I ran some experiments with TCP stream netperf and filebench (having 2 threads performing random reads) benchmarks on an IBM System x3650 M4. I have two machines, A and B. A hosts the vms, B runs the netserver. The vms (on A) run netperf, its destination server is running on B. All runs loaded the guests in a way that they were (cpu) saturated. For example, I ran netperf with 64B messages, which is heavily loading the vm (which is why its throughput is low). The idea was to get it 100% loaded, so we can see that the polling is getting it to produce higher throughput. The system had two cores per guest, as to allow for both the vcpu and the vhost thread to run concurrently for maximum throughput (but I didn't pin the threads to specific cores). My experiments were fair in a sense that for both cases, with or without polling, I run both threads, vcpu and vhost, on 2 cores (set their affinity that way). The only difference was whether polling was enabled/disabled. Results: Netperf, 1 vm: The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 MB/sec). Number of exits/sec decreased 6x. The same improvement was shown when I tested with 3 vms running netperf (4086 MB/sec -> 5545 MB/sec). filebench, 1 vm: ops/sec improved by 13% with the polling patch. Number of exits was reduced by 31%. The same experiment with 3 vms running filebench showed similar numbers. Signed-off-by: Razya Ladelsky --- drivers/vhost/net.c |6 +- drivers/vhost/scsi.c |6 +- drivers/vhost/vhost.c | 245 +++-- drivers/vhost/vhost.h | 38 +++- 4 files changed, 277 insertions(+), 18 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 971a760..558aecb 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -742,8 +742,10 @@ static int vhost_net_open(struct inode *inode, struct file *f) } vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX); - vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, dev); - vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, dev); + vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, + vqs[VHOST_NET_VQ_TX]); + vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, + vqs[VHOST_NET_VQ_RX]); f->private_data = n; diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c index 4f4ffa4..665eeeb 100644 --- a/drivers/vhost/scsi.c +++ b/drivers/vhost/scsi.c @@ -1528,9 +1528,9 @@ static int vhost_scsi_open(struct inode *inode, struct file *f) if (!vqs
Re: [PATCH] vhost: Add polling mode
On 07/21/2014 09:23 PM, Razya Ladelsky wrote: > Hello All, > > When vhost is waiting for buffers from the guest driver (e.g., more > packets > to send in vhost-net's transmit queue), it normally goes to sleep and > waits > for the guest to "kick" it. This kick involves a PIO in the guest, and > therefore an exit (and possibly userspace involvement in translating this > PIO > exit into a file descriptor event), all of which hurts performance. > > If the system is under-utilized (has cpu time to spare), vhost can > continuously poll the virtqueues for new buffers, and avoid asking > the guest to kick us. > This patch adds an optional polling mode to vhost, that can be enabled > via a kernel module parameter, "poll_start_rate". > > When polling is active for a virtqueue, the guest is asked to > disable notification (kicks), and the worker thread continuously checks > for > new buffers. When it does discover new buffers, it simulates a "kick" by > invoking the underlying backend driver (such as vhost-net), which thinks > it > got a real kick from the guest, and acts accordingly. If the underlying > driver asks not to be kicked, we disable polling on this virtqueue. > > We start polling on a virtqueue when we notice it has > work to do. Polling on this virtqueue is later disabled after 3 seconds of > polling turning up no new work, as in this case we are better off > returning > to the exit-based notification mechanism. The default timeout of 3 seconds > can be changed with the "poll_stop_idle" kernel module parameter. > > This polling approach makes lot of sense for new HW with posted-interrupts > for which we have exitless host-to-guest notifications. But even with > support > for posted interrupts, guest-to-host communication still causes exits. > Polling adds the missing part. > > When systems are overloaded, there won?t be enough cpu time for the > various > vhost threads to poll their guests' devices. For these scenarios, we plan > to add support for vhost threads that can be shared by multiple devices, > even of multiple vms. > Our ultimate goal is to implement the I/O acceleration features described > in: > KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) > https://www.youtube.com/watch?v=9EyweibHfEs > and > https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html > > > Comments are welcome, > Thank you, > Razya Thanks for the work. Do you have perf numbers for this? And looks like the patch only poll for virtqueue. In the future, may worth to add callbacks for vhost_net to poll socket. Then it could be used with rx busy polling in host which may speedup the rx also. > > From: Razya Ladelsky > > Add an optional polling mode to continuously poll the virtqueues > for new buffers, and avoid asking the guest to kick us. > > Signed-off-by: Razya Ladelsky > --- > drivers/vhost/net.c |6 +- > drivers/vhost/scsi.c |5 +- > drivers/vhost/vhost.c | 247 > +++-- > drivers/vhost/vhost.h | 37 +++- > 4 files changed, 277 insertions(+), 18 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 971a760..558aecb 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -742,8 +742,10 @@ static int vhost_net_open(struct inode *inode, struct > file *f) > } > vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX); > > - vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, > dev); > - vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, > dev); > + vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, > + vqs[VHOST_NET_VQ_TX]); > + vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, > + vqs[VHOST_NET_VQ_RX]); > > f->private_data = n; > > diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c > index 4f4ffa4..56f0233 100644 > --- a/drivers/vhost/scsi.c > +++ b/drivers/vhost/scsi.c > @@ -1528,9 +1528,8 @@ static int vhost_scsi_open(struct inode *inode, > struct file *f) > if (!vqs) > goto err_vqs; > > - vhost_work_init(&vs->vs_completion_work, > vhost_scsi_complete_cmd_work); > - vhost_work_init(&vs->vs_event_work, tcm_vhost_evt_work); > - > + vhost_work_init(&vs->vs_completion_work, NULL, > vhost_scsi_complete_cmd_work); > + vhost_work_init(&vs->vs_event_work, NULL, tcm_vhost_evt_work); > vs->vs_events_nr = 0; > vs->vs_events_missed = false; > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index c90f437..678d766 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -24,9 +24,17 @@ > #include > #include > #include > +#include > #include > > #include "vhost.h" > +static int poll_start_rate = 0; > +module_param(poll_start_rate, int, S_IRUGO|S_IWUSR); > +MODULE_PARM_DESC(poll_start_rate, "Start continuous polling of virtqueue >
Re: [PATCH] vhost: Add polling mode
Jason Wang wrote on 23/07/2014 08:26:36 AM: > From: Jason Wang > To: Razya Ladelsky/Haifa/IBM@IBMIL, kvm@vger.kernel.org, "Michael S. > Tsirkin" , > Cc: abel.gor...@gmail.com, Joel Nider/Haifa/IBM@IBMIL, Yossi > Kuperman1/Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Alex > Glikson/Haifa/IBM@IBMIL > Date: 23/07/2014 08:26 AM > Subject: Re: [PATCH] vhost: Add polling mode > > On 07/21/2014 09:23 PM, Razya Ladelsky wrote: > > Hello All, > > > > When vhost is waiting for buffers from the guest driver (e.g., more > > packets > > to send in vhost-net's transmit queue), it normally goes to sleep and > > waits > > for the guest to "kick" it. This kick involves a PIO in the guest, and > > therefore an exit (and possibly userspace involvement in translating this > > PIO > > exit into a file descriptor event), all of which hurts performance. > > > > If the system is under-utilized (has cpu time to spare), vhost can > > continuously poll the virtqueues for new buffers, and avoid asking > > the guest to kick us. > > This patch adds an optional polling mode to vhost, that can be enabled > > via a kernel module parameter, "poll_start_rate". > > > > When polling is active for a virtqueue, the guest is asked to > > disable notification (kicks), and the worker thread continuously checks > > for > > new buffers. When it does discover new buffers, it simulates a "kick" by > > invoking the underlying backend driver (such as vhost-net), which thinks > > it > > got a real kick from the guest, and acts accordingly. If the underlying > > driver asks not to be kicked, we disable polling on this virtqueue. > > > > We start polling on a virtqueue when we notice it has > > work to do. Polling on this virtqueue is later disabled after 3 seconds of > > polling turning up no new work, as in this case we are better off > > returning > > to the exit-based notification mechanism. The default timeout of 3 seconds > > can be changed with the "poll_stop_idle" kernel module parameter. > > > > This polling approach makes lot of sense for new HW with posted-interrupts > > for which we have exitless host-to-guest notifications. But even with > > support > > for posted interrupts, guest-to-host communication still causes exits. > > Polling adds the missing part. > > > > When systems are overloaded, there won?t be enough cpu time for the > > various > > vhost threads to poll their guests' devices. For these scenarios, we plan > > to add support for vhost threads that can be shared by multiple devices, > > even of multiple vms. > > Our ultimate goal is to implement the I/O acceleration features described > > in: > > KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) > > https://www.youtube.com/watch?v=9EyweibHfEs > > and > > https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html > > > > > > Comments are welcome, > > Thank you, > > Razya > > Thanks for the work. Do you have perf numbers for this? > Hi Jason, Thanks for reviewing. I ran some experiments with TCP stream netperf and filebench (having 2 threads performing random reads) benchmarks on an IBM System x3650 M4. All runs loaded the guests in a way that they were (cpu) saturated. The system had two cores per guest, as to allow for both the vcpu and the vhost thread to run concurrently for maximum throughput (but I didn't pin the threads to specific cores) I get: Netperf, 1 vm: The polling patch improved throughput by ~33%. Number of exits/sec decreased 6x. The same improvement was shown when I tested with 3 vms running netperf. filebench, 1 vm: ops/sec improved by 13% with the polling patch. Number of exits was reduced by 31%. The same experiment with 3 vms running filebench showed similar numbers. > And looks like the patch only poll for virtqueue. In the future, may > worth to add callbacks for vhost_net to poll socket. Then it could be > used with rx busy polling in host which may speedup the rx also. Did you mean polling the network device to avoid interrupts? > > > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > > index c90f437..678d766 100644 > > --- a/drivers/vhost/vhost.c > > +++ b/drivers/vhost/vhost.c > > @@ -24,9 +24,17 @@ > > #include > > #include > > #include > > +#include > > #include > > > > #include "vhost.h" > > +static int poll_start_rate = 0; > > +module_param(poll_start_rate, int, S_IRUGO|S_IWUSR); > > +MODULE_PARM_DESC(poll_star
Re: [PATCH] vhost: Add polling mode
On 07/23/2014 04:12 PM, Razya Ladelsky wrote: > Jason Wang wrote on 23/07/2014 08:26:36 AM: > >> From: Jason Wang >> To: Razya Ladelsky/Haifa/IBM@IBMIL, kvm@vger.kernel.org, "Michael S. >> Tsirkin" , >> Cc: abel.gor...@gmail.com, Joel Nider/Haifa/IBM@IBMIL, Yossi >> Kuperman1/Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Alex >> Glikson/Haifa/IBM@IBMIL >> Date: 23/07/2014 08:26 AM >> Subject: Re: [PATCH] vhost: Add polling mode >> >> On 07/21/2014 09:23 PM, Razya Ladelsky wrote: >>> Hello All, >>> >>> When vhost is waiting for buffers from the guest driver (e.g., more >>> packets >>> to send in vhost-net's transmit queue), it normally goes to sleep and >>> waits >>> for the guest to "kick" it. This kick involves a PIO in the guest, and >>> therefore an exit (and possibly userspace involvement in translating > this >>> PIO >>> exit into a file descriptor event), all of which hurts performance. >>> >>> If the system is under-utilized (has cpu time to spare), vhost can >>> continuously poll the virtqueues for new buffers, and avoid asking >>> the guest to kick us. >>> This patch adds an optional polling mode to vhost, that can be enabled >>> via a kernel module parameter, "poll_start_rate". >>> >>> When polling is active for a virtqueue, the guest is asked to >>> disable notification (kicks), and the worker thread continuously > checks >>> for >>> new buffers. When it does discover new buffers, it simulates a "kick" > by >>> invoking the underlying backend driver (such as vhost-net), which > thinks >>> it >>> got a real kick from the guest, and acts accordingly. If the > underlying >>> driver asks not to be kicked, we disable polling on this virtqueue. >>> >>> We start polling on a virtqueue when we notice it has >>> work to do. Polling on this virtqueue is later disabled after 3 > seconds of >>> polling turning up no new work, as in this case we are better off >>> returning >>> to the exit-based notification mechanism. The default timeout of 3 > seconds >>> can be changed with the "poll_stop_idle" kernel module parameter. >>> >>> This polling approach makes lot of sense for new HW with > posted-interrupts >>> for which we have exitless host-to-guest notifications. But even with >>> support >>> for posted interrupts, guest-to-host communication still causes exits. >>> Polling adds the missing part. >>> >>> When systems are overloaded, there won?t be enough cpu time for the >>> various >>> vhost threads to poll their guests' devices. For these scenarios, we > plan >>> to add support for vhost threads that can be shared by multiple > devices, >>> even of multiple vms. >>> Our ultimate goal is to implement the I/O acceleration features > described >>> in: >>> KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) >>> https://www.youtube.com/watch?v=9EyweibHfEs >>> and >>> https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html >>> >>> >>> Comments are welcome, >>> Thank you, >>> Razya >> Thanks for the work. Do you have perf numbers for this? >> > Hi Jason, > Thanks for reviewing. I ran some experiments with TCP stream netperf and > filebench (having 2 threads performing random reads) benchmarks on an IBM > System x3650 M4. > All runs loaded the guests in a way that they were (cpu) saturated. > The system had two cores per guest, as to allow for both the vcpu and the > vhost thread to > run concurrently for maximum throughput (but I didn't pin the threads to > specific cores) > I get: > > Netperf, 1 vm: > The polling patch improved throughput by ~33%. Number of exits/sec > decreased 6x. > The same improvement was shown when I tested with 3 vms running netperf. > > filebench, 1 vm: > ops/sec improved by 13% with the polling patch. Number of exits was > reduced by 31%. > The same experiment with 3 vms running filebench showed similar numbers. Looks good, may worth to add the result in the commit log. > >> And looks like the patch only poll for virtqueue. In the future, may >> worth to add callbacks for vhost_net to poll socket. Then it could be >> used with rx busy polling in host which may speedup the rx also. > Did you mean polling the network device to avoid interrupts? Yes, recent linux host support rx bus
Re: [PATCH] vhost: Add polling mode
On Wed, Jul 23, 2014 at 11:42 AM, Jason Wang wrote: > > On 07/23/2014 04:12 PM, Razya Ladelsky wrote: > > Jason Wang wrote on 23/07/2014 08:26:36 AM: > > > >> From: Jason Wang > >> To: Razya Ladelsky/Haifa/IBM@IBMIL, kvm@vger.kernel.org, "Michael S. > >> Tsirkin" , > >> Cc: abel.gor...@gmail.com, Joel Nider/Haifa/IBM@IBMIL, Yossi > >> Kuperman1/Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Alex > >> Glikson/Haifa/IBM@IBMIL > >> Date: 23/07/2014 08:26 AM > >> Subject: Re: [PATCH] vhost: Add polling mode > >> > >> On 07/21/2014 09:23 PM, Razya Ladelsky wrote: > >>> Hello All, > >>> > >>> When vhost is waiting for buffers from the guest driver (e.g., more > >>> packets > >>> to send in vhost-net's transmit queue), it normally goes to sleep and > >>> waits > >>> for the guest to "kick" it. This kick involves a PIO in the guest, and > >>> therefore an exit (and possibly userspace involvement in translating > > this > >>> PIO > >>> exit into a file descriptor event), all of which hurts performance. > >>> > >>> If the system is under-utilized (has cpu time to spare), vhost can > >>> continuously poll the virtqueues for new buffers, and avoid asking > >>> the guest to kick us. > >>> This patch adds an optional polling mode to vhost, that can be enabled > >>> via a kernel module parameter, "poll_start_rate". > >>> > >>> When polling is active for a virtqueue, the guest is asked to > >>> disable notification (kicks), and the worker thread continuously > > checks > >>> for > >>> new buffers. When it does discover new buffers, it simulates a "kick" > > by > >>> invoking the underlying backend driver (such as vhost-net), which > > thinks > >>> it > >>> got a real kick from the guest, and acts accordingly. If the > > underlying > >>> driver asks not to be kicked, we disable polling on this virtqueue. > >>> > >>> We start polling on a virtqueue when we notice it has > >>> work to do. Polling on this virtqueue is later disabled after 3 > > seconds of > >>> polling turning up no new work, as in this case we are better off > >>> returning > >>> to the exit-based notification mechanism. The default timeout of 3 > > seconds > >>> can be changed with the "poll_stop_idle" kernel module parameter. > >>> > >>> This polling approach makes lot of sense for new HW with > > posted-interrupts > >>> for which we have exitless host-to-guest notifications. But even with > >>> support > >>> for posted interrupts, guest-to-host communication still causes exits. > >>> Polling adds the missing part. > >>> > >>> When systems are overloaded, there won?t be enough cpu time for the > >>> various > >>> vhost threads to poll their guests' devices. For these scenarios, we > > plan > >>> to add support for vhost threads that can be shared by multiple > > devices, > >>> even of multiple vms. > >>> Our ultimate goal is to implement the I/O acceleration features > > described > >>> in: > >>> KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) > >>> https://www.youtube.com/watch?v=9EyweibHfEs > >>> and > >>> https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html > >>> > >>> > >>> Comments are welcome, > >>> Thank you, > >>> Razya > >> Thanks for the work. Do you have perf numbers for this? > >> > > Hi Jason, > > Thanks for reviewing. I ran some experiments with TCP stream netperf and > > filebench (having 2 threads performing random reads) benchmarks on an IBM > > System x3650 M4. > > All runs loaded the guests in a way that they were (cpu) saturated. > > The system had two cores per guest, as to allow for both the vcpu and the > > vhost thread to > > run concurrently for maximum throughput (but I didn't pin the threads to > > specific cores) > > I get: > > > > Netperf, 1 vm: > > The polling patch improved throughput by ~33%. Number of exits/sec > > decreased 6x. > > The same improvement was shown when I tested with 3 vms running netperf. > > > > filebench, 1 vm: > > ops/sec improved by 13% with the polling patch. Number
Re: [PATCH] vhost: Add polling mode
On 07/23/2014 04:48 PM, Abel Gordon wrote: > On Wed, Jul 23, 2014 at 11:42 AM, Jason Wang wrote: >> > >> > On 07/23/2014 04:12 PM, Razya Ladelsky wrote: >>> > > Jason Wang wrote on 23/07/2014 08:26:36 AM: >>> > > >>>> > >> From: Jason Wang >>>> > >> To: Razya Ladelsky/Haifa/IBM@IBMIL, kvm@vger.kernel.org, "Michael S. >>>> > >> Tsirkin" , >>>> > >> Cc: abel.gor...@gmail.com, Joel Nider/Haifa/IBM@IBMIL, Yossi >>>> > >> Kuperman1/Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Alex >>>> > >> Glikson/Haifa/IBM@IBMIL >>>> > >> Date: 23/07/2014 08:26 AM >>>> > >> Subject: Re: [PATCH] vhost: Add polling mode >>>> > >> >>>> > >> On 07/21/2014 09:23 PM, Razya Ladelsky wrote: >>>>> > >>> Hello All, >>>>> > >>> >>>>> > >>> When vhost is waiting for buffers from the guest driver (e.g., more >>>>> > >>> packets >>>>> > >>> to send in vhost-net's transmit queue), it normally goes to sleep >>>>> > >>> and >>>>> > >>> waits >>>>> > >>> for the guest to "kick" it. This kick involves a PIO in the guest, >>>>> > >>> and >>>>> > >>> therefore an exit (and possibly userspace involvement in translating >>> > > this >>>>> > >>> PIO >>>>> > >>> exit into a file descriptor event), all of which hurts performance. >>>>> > >>> >>>>> > >>> If the system is under-utilized (has cpu time to spare), vhost can >>>>> > >>> continuously poll the virtqueues for new buffers, and avoid asking >>>>> > >>> the guest to kick us. >>>>> > >>> This patch adds an optional polling mode to vhost, that can be >>>>> > >>> enabled >>>>> > >>> via a kernel module parameter, "poll_start_rate". >>>>> > >>> >>>>> > >>> When polling is active for a virtqueue, the guest is asked to >>>>> > >>> disable notification (kicks), and the worker thread continuously >>> > > checks >>>>> > >>> for >>>>> > >>> new buffers. When it does discover new buffers, it simulates a >>>>> > >>> "kick" >>> > > by >>>>> > >>> invoking the underlying backend driver (such as vhost-net), which >>> > > thinks >>>>> > >>> it >>>>> > >>> got a real kick from the guest, and acts accordingly. If the >>> > > underlying >>>>> > >>> driver asks not to be kicked, we disable polling on this virtqueue. >>>>> > >>> >>>>> > >>> We start polling on a virtqueue when we notice it has >>>>> > >>> work to do. Polling on this virtqueue is later disabled after 3 >>> > > seconds of >>>>> > >>> polling turning up no new work, as in this case we are better off >>>>> > >>> returning >>>>> > >>> to the exit-based notification mechanism. The default timeout of 3 >>> > > seconds >>>>> > >>> can be changed with the "poll_stop_idle" kernel module parameter. >>>>> > >>> >>>>> > >>> This polling approach makes lot of sense for new HW with >>> > > posted-interrupts >>>>> > >>> for which we have exitless host-to-guest notifications. But even >>>>> > >>> with >>>>> > >>> support >>>>> > >>> for posted interrupts, guest-to-host communication still causes >>>>> > >>> exits. >>>>> > >>> Polling adds the missing part. >>>>> > >>> >>>>> > >>> When systems are overloaded, there won?t be enough cpu time for the >>>>> > >>> various >>>>> > >>> vhost threads to poll their guests' devices. For these scenarios, we >>> > > plan >>>>> > >>> to add support for vhost th
Re: [PATCH] vhost: Add polling mode
Maybe tie a knot between "vhost-net scalability tuning: threading for many VMs" and "vhost: Add polling mode" is a good marriage, because it's more possibility to get work to do with less polling time, so less cpu cycles waste. Thanks, Zhang Haoyu >> > >>> Hello All, >> > >>> >> > >>> When vhost is waiting for buffers from the guest driver (e.g., more >> > >>> packets >> > >>> to send in vhost-net's transmit queue), it normally goes to sleep >> > >>> and >> > >>> waits >> > >>> for the guest to "kick" it. This kick involves a PIO in the guest, >> > >>> and >> > >>> therefore an exit (and possibly userspace involvement in >> > >>> translating > > this >> > >>> PIO >> > >>> exit into a file descriptor event), all of which hurts performance. >> > >>> >> > >>> If the system is under-utilized (has cpu time to spare), vhost can >> > >>> continuously poll the virtqueues for new buffers, and avoid asking >> > >>> the guest to kick us. >> > >>> This patch adds an optional polling mode to vhost, that can be >> > >>> enabled >> > >>> via a kernel module parameter, "poll_start_rate". >> > >>> >> > >>> When polling is active for a virtqueue, the guest is asked to >> > >>> disable notification (kicks), and the worker thread continuously > > checks >> > >>> for >> > >>> new buffers. When it does discover new buffers, it simulates a >> > >>> "kick" > > by >> > >>> invoking the underlying backend driver (such as vhost-net), which > > thinks >> > >>> it >> > >>> got a real kick from the guest, and acts accordingly. If the > > underlying >> > >>> driver asks not to be kicked, we disable polling on this virtqueue. >> > >>> >> > >>> We start polling on a virtqueue when we notice it has >> > >>> work to do. Polling on this virtqueue is later disabled after 3 > > seconds of >> > >>> polling turning up no new work, as in this case we are better off >> > >>> returning >> > >>> to the exit-based notification mechanism. The default timeout of 3 > > seconds >> > >>> can be changed with the "poll_stop_idle" kernel module parameter. >> > >>> >> > >>> This polling approach makes lot of sense for new HW with > > posted-interrupts >> > >>> for which we have exitless host-to-guest notifications. But even >> > >>> with >> > >>> support >> > >>> for posted interrupts, guest-to-host communication still causes >> > >>> exits. >> > >>> Polling adds the missing part. >> > >>> >> > >>> When systems are overloaded, there won?t be enough cpu time for the >> > >>> various >> > >>> vhost threads to poll their guests' devices. For these scenarios, >> > >>> we > > plan >> > >>> to add support for vhost threads that can be shared by multiple > > devices, >> > >>> even of multiple vms. >> > >>> Our ultimate goal is to implement the I/O acceleration features > > described >> > >>> in: >> > >>> KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) >> > >>> https://www.youtube.com/watch?v=9EyweibHfEs >> > >>> and >> > >>> https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html >> > >>> >> > >>> >> > >>> Comments are welcome, >> > >>> Thank you, >> > >>> Razya > > >> Thanks for the work. Do you have perf numbers for this? > > >> > > Hi Jason, > > Thanks for reviewing. I ran some experiments with TCP stream netperf > > and > > filebench (having 2 threads performing random reads) benchmarks on an > > IBM > > System x3650 M4. > > All runs loaded the guests in a way that they were (cpu) saturated. > > The system had two cores per guest, as to allow for both the vcpu and > > the > > vhost thread to > > run concurrently for maximum throughput (but I didn't pin the threads > > to > > specific cores) > > I get: > > > > Netperf, 1 vm: > > The polling patch improved throughput by ~33%. Number of exits/sec > > decreased 6x. > > The same improvement was shown when I tested with 3 vms running > > netperf. > > > > filebench, 1 vm: > > ops/sec improved by 13% with the polling patch. Number of exits was > > reduced by 31%. > > The same experiment with 3 vms running filebench showed similar > > numbers. >>> > >>> > Looks good, may worth to add the result in the commit log. > > > > >> And looks like the patch only poll for virtqueue. In the future, may > > >> worth to add callbacks for vhost_net to poll socket. Then it could be > > >> used with rx busy polling in host which may speedup the rx also. > > Did you mean polling the network device to avoid interrupts? >>> > >>> > Yes, recent linux host support rx busy polling which can reduce the >>> > interrupts. If vhost can utilize this,
Re: [PATCH] vhost: Add polling mode
kvm-ow...@vger.kernel.org wrote on 29/07/2014 04:30:34 AM: > From: "Zhang Haoyu" > To: "Jason Wang" , "Abel Gordon" > , > Cc: Razya Ladelsky/Haifa/IBM@IBMIL, Alex Glikson/Haifa/IBM@IBMIL, > Eran Raichstein/Haifa/IBM@IBMIL, Joel Nider/Haifa/IBM@IBMIL, "kvm" > , "Michael S. Tsirkin" , Yossi > Kuperman1/Haifa/IBM@IBMIL > Date: 29/07/2014 04:35 AM > Subject: Re: [PATCH] vhost: Add polling mode > Sent by: kvm-ow...@vger.kernel.org > > Maybe tie a knot between "vhost-net scalability tuning: threading > for many VMs" and "vhost: Add polling mode" is a good marriage, > because it's more possibility to get work to do with less polling > time, so less cpu cycles waste. > Hi Zhang, Indeed have one vhost thread shared by multiple vms, polling for their requests is the ultimate goal of this plan. The current challenge with it is that the cgroup mechanism needs to be supported/incorporated somehow by this shared vhost thread, as it now serves multiple vms(processes). B.T.W. - if someone wants to help with this effort (mainly the cgroup issue), it would be greatly appreciated...! Thank you, Razya > Thanks, > Zhang Haoyu > > >>>>>> > >>> Hello All, > >>>>>> > >>> > >>>>>> > >>> When vhost is waiting for buffers from the guest driver > (e.g., more > >>>>>> > >>> packets > >>>>>> > >>> to send in vhost-net's transmit queue), it normally > goes to sleep and > >>>>>> > >>> waits > >>>>>> > >>> for the guest to "kick" it. This kick involves a PIO in > the guest, and > >>>>>> > >>> therefore an exit (and possibly userspace involvement > in translating > >>>> > > this > >>>>>> > >>> PIO > >>>>>> > >>> exit into a file descriptor event), all of which hurts > performance. > >>>>>> > >>> > >>>>>> > >>> If the system is under-utilized (has cpu time to > spare), vhost can > >>>>>> > >>> continuously poll the virtqueues for new buffers, and > avoid asking > >>>>>> > >>> the guest to kick us. > >>>>>> > >>> This patch adds an optional polling mode to vhost, that > can be enabled > >>>>>> > >>> via a kernel module parameter, "poll_start_rate". > >>>>>> > >>> > >>>>>> > >>> When polling is active for a virtqueue, the guest is asked to > >>>>>> > >>> disable notification (kicks), and the worker thread continuously > >>>> > > checks > >>>>>> > >>> for > >>>>>> > >>> new buffers. When it does discover new buffers, it > simulates a "kick" > >>>> > > by > >>>>>> > >>> invoking the underlying backend driver (such as vhost-net), which > >>>> > > thinks > >>>>>> > >>> it > >>>>>> > >>> got a real kick from the guest, and acts accordingly. If the > >>>> > > underlying > >>>>>> > >>> driver asks not to be kicked, we disable polling on > this virtqueue. > >>>>>> > >>> > >>>>>> > >>> We start polling on a virtqueue when we notice it has > >>>>>> > >>> work to do. Polling on this virtqueue is later disabled after 3 > >>>> > > seconds of > >>>>>> > >>> polling turning up no new work, as in this case we are better off > >>>>>> > >>> returning > >>>>>> > >>> to the exit-based notification mechanism. The default > timeout of 3 > >>>> > > seconds > >>>>>> > >>> can be changed with the "poll_stop_idle" kernel module parameter. > >>>>>> > >>> > >>>>>> > >>> This polling approach makes lot of sense for new HW with > >>>> > > posted-interrupts > >>>>>> > >>> for which we have exitless host-to-guest notifications. > But even with > >>>>>> > >>> support > >>>>>> &
Re: [PATCH] vhost: Add polling mode
On Mon, Jul 21, 2014 at 04:23:44PM +0300, Razya Ladelsky wrote: > Hello All, > > When vhost is waiting for buffers from the guest driver (e.g., more > packets > to send in vhost-net's transmit queue), it normally goes to sleep and > waits > for the guest to "kick" it. This kick involves a PIO in the guest, and > therefore an exit (and possibly userspace involvement in translating this > PIO > exit into a file descriptor event), all of which hurts performance. > > If the system is under-utilized (has cpu time to spare), vhost can > continuously poll the virtqueues for new buffers, and avoid asking > the guest to kick us. > This patch adds an optional polling mode to vhost, that can be enabled > via a kernel module parameter, "poll_start_rate". > > When polling is active for a virtqueue, the guest is asked to > disable notification (kicks), and the worker thread continuously checks > for > new buffers. When it does discover new buffers, it simulates a "kick" by > invoking the underlying backend driver (such as vhost-net), which thinks > it > got a real kick from the guest, and acts accordingly. If the underlying > driver asks not to be kicked, we disable polling on this virtqueue. > > We start polling on a virtqueue when we notice it has > work to do. Polling on this virtqueue is later disabled after 3 seconds of > polling turning up no new work, as in this case we are better off > returning > to the exit-based notification mechanism. The default timeout of 3 seconds > can be changed with the "poll_stop_idle" kernel module parameter. > > This polling approach makes lot of sense for new HW with posted-interrupts > for which we have exitless host-to-guest notifications. But even with > support > for posted interrupts, guest-to-host communication still causes exits. > Polling adds the missing part. > > When systems are overloaded, there won?t be enough cpu time for the > various > vhost threads to poll their guests' devices. For these scenarios, we plan > to add support for vhost threads that can be shared by multiple devices, > even of multiple vms. > Our ultimate goal is to implement the I/O acceleration features described > in: > KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) > https://www.youtube.com/watch?v=9EyweibHfEs > and > https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html > > > Comments are welcome, > Thank you, > Razya > > From: Razya Ladelsky > > Add an optional polling mode to continuously poll the virtqueues > for new buffers, and avoid asking the guest to kick us. > > Signed-off-by: Razya Ladelsky This is an optimization patch, isn't it? Could you please include some numbers showing its effect? > --- > drivers/vhost/net.c |6 +- > drivers/vhost/scsi.c |5 +- > drivers/vhost/vhost.c | 247 > +++-- > drivers/vhost/vhost.h | 37 +++- > 4 files changed, 277 insertions(+), 18 deletions(-) Whitespace seems mangled to the point of making patch unreadable. Can you pls repost? > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 971a760..558aecb 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -742,8 +742,10 @@ static int vhost_net_open(struct inode *inode, struct > file *f) > } > vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX); > > - vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, > dev); > - vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, > dev); > + vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, > + vqs[VHOST_NET_VQ_TX]); > + vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, > + vqs[VHOST_NET_VQ_RX]); > > f->private_data = n; > > diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c > index 4f4ffa4..56f0233 100644 > --- a/drivers/vhost/scsi.c > +++ b/drivers/vhost/scsi.c > @@ -1528,9 +1528,8 @@ static int vhost_scsi_open(struct inode *inode, > struct file *f) > if (!vqs) > goto err_vqs; > > - vhost_work_init(&vs->vs_completion_work, > vhost_scsi_complete_cmd_work); > - vhost_work_init(&vs->vs_event_work, tcm_vhost_evt_work); > - > + vhost_work_init(&vs->vs_completion_work, NULL, > vhost_scsi_complete_cmd_work); > + vhost_work_init(&vs->vs_event_work, NULL, tcm_vhost_evt_work); > vs->vs_events_nr = 0; > vs->vs_events_missed = false; > > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c > index c90f437..678d766 100644 > --- a/drivers/vhost/vhost.c > +++ b/drivers/vhost/vhost.c > @@ -24,9 +24,17 @@ > #include > #include > #include > +#include > #include > > #include "vhost.h" > +static int poll_start_rate = 0; > +module_param(poll_start_rate, int, S_IRUGO|S_IWUSR); > +MODULE_PARM_DESC(poll_start_rate, "Start continuous polling of virtqueue > when rate of events is at least this number
Re: [PATCH] vhost: Add polling mode
"Michael S. Tsirkin" wrote on 29/07/2014 11:06:40 AM: > From: "Michael S. Tsirkin" > To: Razya Ladelsky/Haifa/IBM@IBMIL, > Cc: kvm@vger.kernel.org, abel.gor...@gmail.com, Joel Nider/Haifa/ > IBM@IBMIL, Yossi Kuperman1/Haifa/IBM@IBMIL, Eran Raichstein/Haifa/ > IBM@IBMIL, Alex Glikson/Haifa/IBM@IBMIL > Date: 29/07/2014 11:06 AM > Subject: Re: [PATCH] vhost: Add polling mode > > On Mon, Jul 21, 2014 at 04:23:44PM +0300, Razya Ladelsky wrote: > > Hello All, > > > > When vhost is waiting for buffers from the guest driver (e.g., more > > packets > > to send in vhost-net's transmit queue), it normally goes to sleep and > > waits > > for the guest to "kick" it. This kick involves a PIO in the guest, and > > therefore an exit (and possibly userspace involvement in translating this > > PIO > > exit into a file descriptor event), all of which hurts performance. > > > > If the system is under-utilized (has cpu time to spare), vhost can > > continuously poll the virtqueues for new buffers, and avoid asking > > the guest to kick us. > > This patch adds an optional polling mode to vhost, that can be enabled > > via a kernel module parameter, "poll_start_rate". > > > > When polling is active for a virtqueue, the guest is asked to > > disable notification (kicks), and the worker thread continuously checks > > for > > new buffers. When it does discover new buffers, it simulates a "kick" by > > invoking the underlying backend driver (such as vhost-net), which thinks > > it > > got a real kick from the guest, and acts accordingly. If the underlying > > driver asks not to be kicked, we disable polling on this virtqueue. > > > > We start polling on a virtqueue when we notice it has > > work to do. Polling on this virtqueue is later disabled after 3 seconds of > > polling turning up no new work, as in this case we are better off > > returning > > to the exit-based notification mechanism. The default timeout of 3 seconds > > can be changed with the "poll_stop_idle" kernel module parameter. > > > > This polling approach makes lot of sense for new HW with posted-interrupts > > for which we have exitless host-to-guest notifications. But even with > > support > > for posted interrupts, guest-to-host communication still causes exits. > > Polling adds the missing part. > > > > When systems are overloaded, there won?t be enough cpu time for the > > various > > vhost threads to poll their guests' devices. For these scenarios, we plan > > to add support for vhost threads that can be shared by multiple devices, > > even of multiple vms. > > Our ultimate goal is to implement the I/O acceleration features described > > in: > > KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) > > https://www.youtube.com/watch?v=9EyweibHfEs > > and > > https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html > > > > > > Comments are welcome, > > Thank you, > > Razya > > > > From: Razya Ladelsky > > > > Add an optional polling mode to continuously poll the virtqueues > > for new buffers, and avoid asking the guest to kick us. > > > > Signed-off-by: Razya Ladelsky > > This is an optimization patch, isn't it? > Could you please include some numbers showing its > effect? > > Hi Michael, Sure. I included them in a reply to Jason Wang in this thread, Here it is: http://www.spinics.net/linux/lists/kvm/msg106049.html > > --- > > drivers/vhost/net.c |6 +- > > drivers/vhost/scsi.c |5 +- > > drivers/vhost/vhost.c | 247 > > +++-- > > drivers/vhost/vhost.h | 37 +++- > > 4 files changed, 277 insertions(+), 18 deletions(-) > > > Whitespace seems mangled to the point of making patch > unreadable. Can you pls repost? > Sure. > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > > index 971a760..558aecb 100644 > > --- a/drivers/vhost/net.c > > +++ b/drivers/vhost/net.c > > @@ -742,8 +742,10 @@ static int vhost_net_open(struct inode *inode, struct > > file *f) > > } > > vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX); > > > > - vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle_tx_net, POLLOUT, > > dev); > > - vhost_poll_init(n->poll + VHOST_NET_VQ_RX, handle_rx_net, POLLIN, > > dev); > > + vhost_poll_init(n->poll + VHOST_NET_VQ_TX, handle
Re: [PATCH] vhost: Add polling mode
On Tue, Jul 29, 2014 at 01:30:03PM +0300, Razya Ladelsky wrote: [..] had to snip off the quoted text, it's mangled up to unreadability. Please take a look at Documentation/email-clients.txt to fix this. > > This is an optimization patch, isn't it? > > Could you please include some numbers showing its > > effect? > > > > > > Hi Michael, > Sure. I included them in a reply to Jason Wang in this thread, > Here it is: > http://www.spinics.net/linux/lists/kvm/msg106049.html > Hmm there aren't a lot of numbers there :(. Speed increased by 33% but by how much? E.g. maybe you are getting from 1Mbyte/sec to 1.3, if so it's hard to get excited about it. Some questions that come to mind: what was the message size? I would expect several measurements with different values. How did host CPU utilization change? What about latency? As we are competing with guest for host CPU, would worst-case or average latency suffer? Thanks, -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
> > Hmm there aren't a lot of numbers there :(. Speed increased by 33% but > by how much? E.g. maybe you are getting from 1Mbyte/sec to 1.3, > if so it's hard to get excited about it. Netperf 1 VM: 1516 MB/sec -> 2046 MB/sec and for 3 VMs: 4086 MB/sec -> 5545 MB/sec > Some questions that come to > mind: what was the message size? I would expect several measurements > with different values. How did host CPU utilization change? > message size was 64B in order to get the VM to be cpu saturated. so vhost had 99% cpu and vhost 38%, with the polling patch both had 99%. > What about latency? As we are competing with guest for host CPU, > would worst-case or average latency suffer? > Polling indeed doesn't make a lot of sense if there aren't enough available cores. In these cases polling should not be used. Thank you, Razya > Thanks, > > -- > MST > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
On Tue, Jul 29, 2014 at 03:23:59PM +0300, Razya Ladelsky wrote: > > > > Hmm there aren't a lot of numbers there :(. Speed increased by 33% but > > by how much? E.g. maybe you are getting from 1Mbyte/sec to 1.3, > > if so it's hard to get excited about it. > > Netperf 1 VM: 1516 MB/sec -> 2046 MB/sec > and for 3 VMs: 4086 MB/sec -> 5545 MB/sec What do you mean by 1 VM? Streaming TCP host to vm? Also, your throughput is somewhat low, it's worth seeing why you can't hit higher speeds. > > Some questions that come to > > mind: what was the message size? I would expect several measurements > > with different values. How did host CPU utilization change? > > > > message size was 64B in order to get the VM to be cpu saturated. > so vhost had 99% cpu and vhost 38%, with the polling patch both had 99%. Hmm so a net loss in throughput/CPU. > > > > What about latency? As we are competing with guest for host CPU, > > would worst-case or average latency suffer? > > > > Polling indeed doesn't make a lot of sense if there aren't enough > available cores. > In these cases polling should not be used. > > Thank you, > Razya OK but scheduler might run vm and vhost on the same cpu even if cores are available. This needs to be detected somehow and polling disabled. > > > > Thanks, > > > > -- > > MST > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > the body of a message to majord...@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
kvm-ow...@vger.kernel.org wrote on 29/07/2014 03:40:18 PM: > From: "Michael S. Tsirkin" > To: Razya Ladelsky/Haifa/IBM@IBMIL, > Cc: abel.gor...@gmail.com, Alex Glikson/Haifa/IBM@IBMIL, Eran > Raichstein/Haifa/IBM@IBMIL, Joel Nider/Haifa/IBM@IBMIL, > kvm@vger.kernel.org, kvm-ow...@vger.kernel.org, Yossi Kuperman1/ > Haifa/IBM@IBMIL > Date: 29/07/2014 03:40 PM > Subject: Re: [PATCH] vhost: Add polling mode > Sent by: kvm-ow...@vger.kernel.org > > On Tue, Jul 29, 2014 at 03:23:59PM +0300, Razya Ladelsky wrote: > > > > > > Hmm there aren't a lot of numbers there :(. Speed increased by 33% but > > > by how much? E.g. maybe you are getting from 1Mbyte/sec to 1.3, > > > if so it's hard to get excited about it. > > > > Netperf 1 VM: 1516 MB/sec -> 2046 MB/sec > > and for 3 VMs: 4086 MB/sec -> 5545 MB/sec > > What do you mean by 1 VM? Streaming TCP host to vm? > Also, your throughput is somewhat low, it's worth seeing > why you can't hit higher speeds. > My configuration is this: I have two machines, A and B. A hosts the vms, B runs the netserver. One vm (on A) runs netperf, where the its destination server is running on B. I ran netperf with 64B messages, which is heavily loading the vm, which is why its throughput is low. The idea was to get it 100% loaded, so we can see that the polling is getting it to produce higher throughput. > > > Some questions that come to > > > mind: what was the message size? I would expect several measurements > > > with different values. How did host CPU utilization change? > > > > > > > message size was 64B in order to get the VM to be cpu saturated. > > so vhost had 99% cpu and vhost 38%, with the polling patch both had 99%. > > Hmm so a net loss in throughput/CPU. > Actually, my experiments were fair in a sense that for both cases, with or without polling, I run both threads, vcpu and vhost, on 2 cores (set their affinity that way). The only difference was whether polling was enabled/disabled. > > > > > > > What about latency? As we are competing with guest for host CPU, > > > would worst-case or average latency suffer? > > > > > > > Polling indeed doesn't make a lot of sense if there aren't enough > > available cores. > > In these cases polling should not be used. > > > > Thank you, > > Razya > > OK but scheduler might run vm and vhost on the same cpu > even if cores are available. > This needs to be detected somehow and polling disabled. > > > > > > > > > Thanks, > > > > > > -- > > > MST > > > -- > > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > > the body of a message to majord...@vger.kernel.org > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
On Sun, Aug 10, 2014 at 11:30:35AM +0300, Razya Ladelsky wrote: > From: Razya Ladelsky > Date: Thu, 31 Jul 2014 09:47:20 +0300 > Subject: [PATCH] vhost: Add polling mode > > When vhost is waiting for buffers from the guest driver (e.g., more packets to > send in vhost-net's transmit queue), it normally goes to sleep and waits for > the > guest to "kick" it. This kick involves a PIO in the guest, and therefore an > exit > (and possibly userspace involvement in translating this PIO exit into a file > descriptor event), all of which hurts performance. > > If the system is under-utilized (has cpu time to spare), vhost can > continuously > poll the virtqueues for new buffers, and avoid asking the guest to kick us. > This patch adds an optional polling mode to vhost, that can be enabled via a > kernel module parameter, "poll_start_rate". > > When polling is active for a virtqueue, the guest is asked to disable > notification (kicks), and the worker thread continuously checks for new > buffers. > When it does discover new buffers, it simulates a "kick" by invoking the > underlying backend driver (such as vhost-net), which thinks it got a real kick > from the guest, and acts accordingly. If the underlying driver asks not to be > kicked, we disable polling on this virtqueue. > > We start polling on a virtqueue when we notice it has work to do. Polling on > this virtqueue is later disabled after 3 seconds of polling turning up no new > work, as in this case we are better off returning to the exit-based > notification > mechanism. The default timeout of 3 seconds can be changed with the > "poll_stop_idle" kernel module parameter. > > This polling approach makes lot of sense for new HW with posted-interrupts for > which we have exitless host-to-guest notifications. But even with support for > posted interrupts, guest-to-host communication still causes exits. Polling > adds > the missing part. > > When systems are overloaded, there won't be enough cpu time for the various > vhost threads to poll their guests' devices. For these scenarios, we plan to > add > support for vhost threads that can be shared by multiple devices, even of > multiple vms. > Our ultimate goal is to implement the I/O acceleration features described in: > KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) > https://www.youtube.com/watch?v=9EyweibHfEs > and > https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html > > I ran some experiments with TCP stream netperf and filebench (having 2 threads > performing random reads) benchmarks on an IBM System x3650 M4. > I have two machines, A and B. A hosts the vms, B runs the netserver. > The vms (on A) run netperf, its destination server is running on B. > All runs loaded the guests in a way that they were (cpu) saturated. For > example, > I ran netperf with 64B messages, which is heavily loading the vm (which is why > its throughput is low). > The idea was to get it 100% loaded, so we can see that the polling is getting > it > to produce higher throughput. And, did your tests actually produce 100% load on both host CPUs? > The system had two cores per guest, as to allow for both the vcpu and the > vhost > thread to run concurrently for maximum throughput (but I didn't pin the > threads > to specific cores). > My experiments were fair in a sense that for both cases, with or without > polling, I run both threads, vcpu and vhost, on 2 cores (set their affinity > that > way). The only difference was whether polling was enabled/disabled. > > Results: > > Netperf, 1 vm: > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 MB/sec). > Number of exits/sec decreased 6x. > The same improvement was shown when I tested with 3 vms running netperf > (4086 MB/sec -> 5545 MB/sec). > > filebench, 1 vm: > ops/sec improved by 13% with the polling patch. Number of exits was reduced by > 31%. > The same experiment with 3 vms running filebench showed similar numbers. > > Signed-off-by: Razya Ladelsky > --- > drivers/vhost/net.c |6 +- > drivers/vhost/scsi.c |6 +- > drivers/vhost/vhost.c | 245 > +++-- > drivers/vhost/vhost.h | 38 +++- > 4 files changed, 277 insertions(+), 18 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 971a760..558aecb 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -742,8 +742,10 @@ static int vhost_net_open(struct inode *inode, struct > file *f) > } > vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX); > > - vhost_poll_init(n->poll + VHOST
Re: [PATCH] vhost: Add polling mode
From: "Michael S. Tsirkin" Date: Sun, 10 Aug 2014 21:45:59 +0200 > On Sun, Aug 10, 2014 at 11:30:35AM +0300, Razya Ladelsky wrote: ... > And, did your tests actually produce 100% load on both host CPUs? ... Michael, please do not quote an entire patch just to ask a one line question. I truly, truly, wish it was simpler in modern email clients to delete the unrelated quoted material because I bet when people do this they are simply being lazy. Thank you. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
On Mon, Aug 11, 2014 at 12:46:21PM -0700, David Miller wrote: > From: "Michael S. Tsirkin" > Date: Sun, 10 Aug 2014 21:45:59 +0200 > > > On Sun, Aug 10, 2014 at 11:30:35AM +0300, Razya Ladelsky wrote: > ... > > And, did your tests actually produce 100% load on both host CPUs? > ... > > Michael, please do not quote an entire patch just to ask a one line > question. > > I truly, truly, wish it was simpler in modern email clients to delete > the unrelated quoted material because I bet when people do this they > are simply being lazy. > > Thank you. Lazy - mea culpa, though I'm using mutt so it isn't even hard. The question still stands: the test results are only valid if CPU was at 100% in all configurations. This is the reason I generally prefer it when people report throughput divided by CPU (power would be good too but it still isn't easy for people to get that number). -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
"Michael S. Tsirkin" wrote on 12/08/2014 12:18:50 PM: > From: "Michael S. Tsirkin" > To: David Miller > Cc: Razya Ladelsky/Haifa/IBM@IBMIL, kvm@vger.kernel.org, Alex > Glikson/Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Yossi > Kuperman1/Haifa/IBM@IBMIL, Joel Nider/Haifa/IBM@IBMIL, > abel.gor...@gmail.com, linux-ker...@vger.kernel.org, > net...@vger.kernel.org, virtualizat...@lists.linux-foundation.org > Date: 12/08/2014 12:18 PM > Subject: Re: [PATCH] vhost: Add polling mode > > On Mon, Aug 11, 2014 at 12:46:21PM -0700, David Miller wrote: > > From: "Michael S. Tsirkin" > > Date: Sun, 10 Aug 2014 21:45:59 +0200 > > > > > On Sun, Aug 10, 2014 at 11:30:35AM +0300, Razya Ladelsky wrote: > > ... > > > And, did your tests actually produce 100% load on both host CPUs? > > ... > > > > Michael, please do not quote an entire patch just to ask a one line > > question. > > > > I truly, truly, wish it was simpler in modern email clients to delete > > the unrelated quoted material because I bet when people do this they > > are simply being lazy. > > > > Thank you. > > Lazy - mea culpa, though I'm using mutt so it isn't even hard. > > The question still stands: the test results are only valid > if CPU was at 100% in all configurations. > This is the reason I generally prefer it when people report > throughput divided by CPU (power would be good too but it still > isn't easy for people to get that number). > Hi Michael, Sorry for the delay, had some problems with my mailbox, and I realized just now that my reply wasn't sent. The vm indeed ALWAYS utilized 100% cpu, whether polling was enabled or not. The vhost thread utilized less than 100% (of the other cpu) when polling was disabled. Enabling polling increased its utilization to 100% (in which case both cpus were 100% utilized). > -- > MST > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
On Tue, Aug 12, 2014 at 01:57:05PM +0300, Razya Ladelsky wrote: > "Michael S. Tsirkin" wrote on 12/08/2014 12:18:50 PM: > > > From: "Michael S. Tsirkin" > > To: David Miller > > Cc: Razya Ladelsky/Haifa/IBM@IBMIL, kvm@vger.kernel.org, Alex > > Glikson/Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Yossi > > Kuperman1/Haifa/IBM@IBMIL, Joel Nider/Haifa/IBM@IBMIL, > > abel.gor...@gmail.com, linux-ker...@vger.kernel.org, > > net...@vger.kernel.org, virtualizat...@lists.linux-foundation.org > > Date: 12/08/2014 12:18 PM > > Subject: Re: [PATCH] vhost: Add polling mode > > > > On Mon, Aug 11, 2014 at 12:46:21PM -0700, David Miller wrote: > > > From: "Michael S. Tsirkin" > > > Date: Sun, 10 Aug 2014 21:45:59 +0200 > > > > > > > On Sun, Aug 10, 2014 at 11:30:35AM +0300, Razya Ladelsky wrote: > > > ... > > > > And, did your tests actually produce 100% load on both host CPUs? > > > ... > > > > > > Michael, please do not quote an entire patch just to ask a one line > > > question. > > > > > > I truly, truly, wish it was simpler in modern email clients to delete > > > the unrelated quoted material because I bet when people do this they > > > are simply being lazy. > > > > > > Thank you. > > > > Lazy - mea culpa, though I'm using mutt so it isn't even hard. > > > > The question still stands: the test results are only valid > > if CPU was at 100% in all configurations. > > This is the reason I generally prefer it when people report > > throughput divided by CPU (power would be good too but it still > > isn't easy for people to get that number). > > > > Hi Michael, > > Sorry for the delay, had some problems with my mailbox, and I realized > just now that > my reply wasn't sent. > The vm indeed ALWAYS utilized 100% cpu, whether polling was enabled or > not. > The vhost thread utilized less than 100% (of the other cpu) when polling > was disabled. > Enabling polling increased its utilization to 100% (in which case both > cpus were 100% utilized). Hmm this means the testing wasn't successful then, as you said: The idea was to get it 100% loaded, so we can see that the polling is getting it to produce higher throughput. in fact here you are producing more throughput but spending more power to produce it, which can have any number of explanations besides polling improving the efficiency. For example, increasing system load might disable host power management. > > -- > > MST > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
> > > > Hi Michael, > > > > Sorry for the delay, had some problems with my mailbox, and I realized > > just now that > > my reply wasn't sent. > > The vm indeed ALWAYS utilized 100% cpu, whether polling was enabled or > > not. > > The vhost thread utilized less than 100% (of the other cpu) when polling > > was disabled. > > Enabling polling increased its utilization to 100% (in which case both > > cpus were 100% utilized). > > Hmm this means the testing wasn't successful then, as you said: > >The idea was to get it 100% loaded, so we can see that the polling is >getting it to produce higher throughput. > > in fact here you are producing more throughput but spending more power > to produce it, which can have any number of explanations besides polling > improving the efficiency. For example, increasing system load might > disable host power management. > Hi Michael, I re-ran the tests, this time with the "turbo mode" and "C-states" features off. No Polling: 1 VM running netperf (msg size 64B): 1107 Mbits/sec Polling: 1 VM running netperf (msg size 64B): 1572 Mbits/sec As you can see from the new results, the numbers are lower, but relatively (polling on/off) there's no change. Thank you, Razya > > > > -- > > > MST > > > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
On Sun, Aug 17, 2014 at 03:35:39PM +0300, Razya Ladelsky wrote: > > > > > > Hi Michael, > > > > > > Sorry for the delay, had some problems with my mailbox, and I realized > > > > just now that > > > my reply wasn't sent. > > > The vm indeed ALWAYS utilized 100% cpu, whether polling was enabled or > > > > not. > > > The vhost thread utilized less than 100% (of the other cpu) when > polling > > > was disabled. > > > Enabling polling increased its utilization to 100% (in which case both > > > > cpus were 100% utilized). > > > > Hmm this means the testing wasn't successful then, as you said: > > > >The idea was to get it 100% loaded, so we can see that the polling is > >getting it to produce higher throughput. > > > > in fact here you are producing more throughput but spending more power > > to produce it, which can have any number of explanations besides polling > > improving the efficiency. For example, increasing system load might > > disable host power management. > > > > Hi Michael, > I re-ran the tests, this time with the "turbo mode" and "C-states" > features off. > No Polling: > 1 VM running netperf (msg size 64B): 1107 Mbits/sec > Polling: > 1 VM running netperf (msg size 64B): 1572 Mbits/sec > > > > > > > > As you can see from the new results, the numbers are lower, > but relatively (polling on/off) there's no change. > Thank you, > Razya That was just one example. There many other possibilities. Either actually make the systems load all host CPUs equally, or divide throughput by host CPU. > > > > > > > > > > > -- > > > > MST > > > > > > -- > > To unsubscribe from this list: send the line "unsubscribe kvm" in > > the body of a message to majord...@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
> That was just one example. There many other possibilities. Either > actually make the systems load all host CPUs equally, or divide > throughput by host CPU. > The polling patch adds this capability to vhost, reducing costly exit overhead when the vm is loaded. In order to load the vm I ran netperf with msg size of 256: Without polling: 2480 Mbits/sec, utilization: vm - 100% vhost - 64% With Polling: 4160 Mbits/sec, utilization: vm - 100% vhost - 100% Therefore, throughput/cpu without polling is 15.1, and 20.8 with polling. My intention was to load vhost as close as possible to 100% utilization without polling, in order to compare it to the polling utilization case (where vhost is always 100%). The best use case, of course, would be when the shared vhost thread work (TBD) is integrated and then vhost will actually be using its polling cycles to handle requests of multiple devices (even from multiple vms). Thanks, Razya -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
On 10/08/14 10:30, Razya Ladelsky wrote: > From: Razya Ladelsky > Date: Thu, 31 Jul 2014 09:47:20 +0300 > Subject: [PATCH] vhost: Add polling mode > > When vhost is waiting for buffers from the guest driver (e.g., more packets to > send in vhost-net's transmit queue), it normally goes to sleep and waits for > the > guest to "kick" it. This kick involves a PIO in the guest, and therefore an > exit > (and possibly userspace involvement in translating this PIO exit into a file > descriptor event), all of which hurts performance. > > If the system is under-utilized (has cpu time to spare), vhost can > continuously > poll the virtqueues for new buffers, and avoid asking the guest to kick us. > This patch adds an optional polling mode to vhost, that can be enabled via a > kernel module parameter, "poll_start_rate". > > When polling is active for a virtqueue, the guest is asked to disable > notification (kicks), and the worker thread continuously checks for new > buffers. > When it does discover new buffers, it simulates a "kick" by invoking the > underlying backend driver (such as vhost-net), which thinks it got a real kick > from the guest, and acts accordingly. If the underlying driver asks not to be > kicked, we disable polling on this virtqueue. > > We start polling on a virtqueue when we notice it has work to do. Polling on > this virtqueue is later disabled after 3 seconds of polling turning up no new > work, as in this case we are better off returning to the exit-based > notification > mechanism. The default timeout of 3 seconds can be changed with the > "poll_stop_idle" kernel module parameter. > > This polling approach makes lot of sense for new HW with posted-interrupts for > which we have exitless host-to-guest notifications. But even with support for > posted interrupts, guest-to-host communication still causes exits. Polling > adds > the missing part. > > When systems are overloaded, there won't be enough cpu time for the various > vhost threads to poll their guests' devices. For these scenarios, we plan to > add > support for vhost threads that can be shared by multiple devices, even of > multiple vms. > Our ultimate goal is to implement the I/O acceleration features described in: > KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) > https://www.youtube.com/watch?v=9EyweibHfEs > and > https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html > > I ran some experiments with TCP stream netperf and filebench (having 2 threads > performing random reads) benchmarks on an IBM System x3650 M4. > I have two machines, A and B. A hosts the vms, B runs the netserver. > The vms (on A) run netperf, its destination server is running on B. > All runs loaded the guests in a way that they were (cpu) saturated. For > example, > I ran netperf with 64B messages, which is heavily loading the vm (which is why > its throughput is low). > The idea was to get it 100% loaded, so we can see that the polling is getting > it > to produce higher throughput. > > The system had two cores per guest, as to allow for both the vcpu and the > vhost > thread to run concurrently for maximum throughput (but I didn't pin the > threads > to specific cores). > My experiments were fair in a sense that for both cases, with or without > polling, I run both threads, vcpu and vhost, on 2 cores (set their affinity > that > way). The only difference was whether polling was enabled/disabled. > > Results: > > Netperf, 1 vm: > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 MB/sec). > Number of exits/sec decreased 6x. > The same improvement was shown when I tested with 3 vms running netperf > (4086 MB/sec -> 5545 MB/sec). > > filebench, 1 vm: > ops/sec improved by 13% with the polling patch. Number of exits was reduced by > 31%. > The same experiment with 3 vms running filebench showed similar numbers. > > Signed-off-by: Razya Ladelsky Gave it a quick try on s390/kvm. As expected it makes no difference for big streaming workload like iperf. uperf with a 1-1 round robin got indeed faster by about 30%. The high CPU consumption is something that bothers me though, as virtualized systems tend to be full. > +static int poll_start_rate = 0; > +module_param(poll_start_rate, int, S_IRUGO|S_IWUSR); > +MODULE_PARM_DESC(poll_start_rate, "Start continuous polling of virtqueue > when rate of events is at least this number per jiffy. If 0, never start > polling."); > + > +static int poll_stop_idle = 3*HZ; /* 3 seconds */ > +module_param(poll_stop_idle, int, S_IRUGO|S_IWUSR); > +MODULE_PARM_DESC(poll_stop_idle, "Stop continuous polling
Re: [PATCH] vhost: Add polling mode
On Wed, Aug 20, 2014 at 10:41:32AM +0200, Christian Borntraeger wrote: > On 10/08/14 10:30, Razya Ladelsky wrote: > > From: Razya Ladelsky > > Date: Thu, 31 Jul 2014 09:47:20 +0300 > > Subject: [PATCH] vhost: Add polling mode > > > > When vhost is waiting for buffers from the guest driver (e.g., more packets > > to > > send in vhost-net's transmit queue), it normally goes to sleep and waits > > for the > > guest to "kick" it. This kick involves a PIO in the guest, and therefore an > > exit > > (and possibly userspace involvement in translating this PIO exit into a file > > descriptor event), all of which hurts performance. > > > > If the system is under-utilized (has cpu time to spare), vhost can > > continuously > > poll the virtqueues for new buffers, and avoid asking the guest to kick us. > > This patch adds an optional polling mode to vhost, that can be enabled via a > > kernel module parameter, "poll_start_rate". > > > > When polling is active for a virtqueue, the guest is asked to disable > > notification (kicks), and the worker thread continuously checks for new > > buffers. > > When it does discover new buffers, it simulates a "kick" by invoking the > > underlying backend driver (such as vhost-net), which thinks it got a real > > kick > > from the guest, and acts accordingly. If the underlying driver asks not to > > be > > kicked, we disable polling on this virtqueue. > > > > We start polling on a virtqueue when we notice it has work to do. Polling on > > this virtqueue is later disabled after 3 seconds of polling turning up no > > new > > work, as in this case we are better off returning to the exit-based > > notification > > mechanism. The default timeout of 3 seconds can be changed with the > > "poll_stop_idle" kernel module parameter. > > > > This polling approach makes lot of sense for new HW with posted-interrupts > > for > > which we have exitless host-to-guest notifications. But even with support > > for > > posted interrupts, guest-to-host communication still causes exits. Polling > > adds > > the missing part. > > > > When systems are overloaded, there won't be enough cpu time for the various > > vhost threads to poll their guests' devices. For these scenarios, we plan > > to add > > support for vhost threads that can be shared by multiple devices, even of > > multiple vms. > > Our ultimate goal is to implement the I/O acceleration features described > > in: > > KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) > > https://www.youtube.com/watch?v=9EyweibHfEs > > and > > https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html > > > > I ran some experiments with TCP stream netperf and filebench (having 2 > > threads > > performing random reads) benchmarks on an IBM System x3650 M4. > > I have two machines, A and B. A hosts the vms, B runs the netserver. > > The vms (on A) run netperf, its destination server is running on B. > > All runs loaded the guests in a way that they were (cpu) saturated. For > > example, > > I ran netperf with 64B messages, which is heavily loading the vm (which is > > why > > its throughput is low). > > The idea was to get it 100% loaded, so we can see that the polling is > > getting it > > to produce higher throughput. > > > > The system had two cores per guest, as to allow for both the vcpu and the > > vhost > > thread to run concurrently for maximum throughput (but I didn't pin the > > threads > > to specific cores). > > My experiments were fair in a sense that for both cases, with or without > > polling, I run both threads, vcpu and vhost, on 2 cores (set their affinity > > that > > way). The only difference was whether polling was enabled/disabled. > > > > Results: > > > > Netperf, 1 vm: > > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 MB/sec). > > Number of exits/sec decreased 6x. > > The same improvement was shown when I tested with 3 vms running netperf > > (4086 MB/sec -> 5545 MB/sec). > > > > filebench, 1 vm: > > ops/sec improved by 13% with the polling patch. Number of exits was reduced > > by > > 31%. > > The same experiment with 3 vms running filebench showed similar numbers. > > > > Signed-off-by: Razya Ladelsky > > Gave it a quick try on s390/kvm. As expected it makes no difference for big > streaming workload like iperf. >
Re: [PATCH] vhost: Add polling mode
On Sun, Aug 10, 2014 at 11:30:35AM +0300, Razya Ladelsky wrote: > From: Razya Ladelsky > Date: Thu, 31 Jul 2014 09:47:20 +0300 > Subject: [PATCH] vhost: Add polling mode > > When vhost is waiting for buffers from the guest driver (e.g., more packets to > send in vhost-net's transmit queue), it normally goes to sleep and waits for > the > guest to "kick" it. This kick involves a PIO in the guest, and therefore an > exit > (and possibly userspace involvement in translating this PIO exit into a file > descriptor event), all of which hurts performance. > > If the system is under-utilized (has cpu time to spare), vhost can > continuously > poll the virtqueues for new buffers, and avoid asking the guest to kick us. > This patch adds an optional polling mode to vhost, that can be enabled via a > kernel module parameter, "poll_start_rate". > > When polling is active for a virtqueue, the guest is asked to disable > notification (kicks), and the worker thread continuously checks for new > buffers. > When it does discover new buffers, it simulates a "kick" by invoking the > underlying backend driver (such as vhost-net), which thinks it got a real kick > from the guest, and acts accordingly. If the underlying driver asks not to be > kicked, we disable polling on this virtqueue. > > We start polling on a virtqueue when we notice it has work to do. Polling on > this virtqueue is later disabled after 3 seconds of polling turning up no new > work, as in this case we are better off returning to the exit-based > notification > mechanism. The default timeout of 3 seconds can be changed with the > "poll_stop_idle" kernel module parameter. > > This polling approach makes lot of sense for new HW with posted-interrupts for > which we have exitless host-to-guest notifications. But even with support for > posted interrupts, guest-to-host communication still causes exits. Polling > adds > the missing part. > > When systems are overloaded, there won't be enough cpu time for the various > vhost threads to poll their guests' devices. For these scenarios, we plan to > add > support for vhost threads that can be shared by multiple devices, even of > multiple vms. > Our ultimate goal is to implement the I/O acceleration features described in: > KVM Forum 2013: Efficient and Scalable Virtio (by Abel Gordon) > https://www.youtube.com/watch?v=9EyweibHfEs > and > https://www.mail-archive.com/kvm@vger.kernel.org/msg98179.html > > I ran some experiments with TCP stream netperf and filebench (having 2 threads > performing random reads) benchmarks on an IBM System x3650 M4. > I have two machines, A and B. A hosts the vms, B runs the netserver. > The vms (on A) run netperf, its destination server is running on B. > All runs loaded the guests in a way that they were (cpu) saturated. For > example, > I ran netperf with 64B messages, which is heavily loading the vm (which is why > its throughput is low). > The idea was to get it 100% loaded, so we can see that the polling is getting > it > to produce higher throughput. > > The system had two cores per guest, as to allow for both the vcpu and the > vhost > thread to run concurrently for maximum throughput (but I didn't pin the > threads > to specific cores). > My experiments were fair in a sense that for both cases, with or without > polling, I run both threads, vcpu and vhost, on 2 cores (set their affinity > that > way). The only difference was whether polling was enabled/disabled. > > Results: > > Netperf, 1 vm: > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 MB/sec). > Number of exits/sec decreased 6x. > The same improvement was shown when I tested with 3 vms running netperf > (4086 MB/sec -> 5545 MB/sec). > > filebench, 1 vm: > ops/sec improved by 13% with the polling patch. Number of exits was reduced by > 31%. > The same experiment with 3 vms running filebench showed similar numbers. > > Signed-off-by: Razya Ladelsky This really needs more thourough benchmarking report, including system data. One good example for a related patch: http://lwn.net/Articles/551179/ though for virtualization, we need data about host as well, and if you want to look at streaming benchmarks, you need to test different message sizes and measure packet size. For now, commenting on the patches assuming that will be forthcoming. > --- > drivers/vhost/net.c |6 +- > drivers/vhost/scsi.c |6 +- > drivers/vhost/vhost.c | 245 > +++-- > drivers/vhost/vhost.h | 38 +++- > 4 files changed, 277 insertions(+), 18 deletions(-) > > diff --git a/drivers/vhos
Re: [PATCH] vhost: Add polling mode
On Tue, Aug 19, 2014 at 11:36:31AM +0300, Razya Ladelsky wrote: > > That was just one example. There many other possibilities. Either > > actually make the systems load all host CPUs equally, or divide > > throughput by host CPU. > > > > The polling patch adds this capability to vhost, reducing costly exit > overhead when the vm is loaded. > > In order to load the vm I ran netperf with msg size of 256: > > Without polling: 2480 Mbits/sec, utilization: vm - 100% vhost - 64% > With Polling: 4160 Mbits/sec, utilization: vm - 100% vhost - 100% > > Therefore, throughput/cpu without polling is 15.1, and 20.8 with polling. > Can you please present results in a form that makes it possible to see the effect on various configurations and workloads? Here's one example where this was done: https://lkml.org/lkml/2014/8/14/495 You really should also provide data about your host configuration (missing in the above link). > My intention was to load vhost as close as possible to 100% utilization > without polling, in order to compare it to the polling utilization case > (where vhost is always 100%). > The best use case, of course, would be when the shared vhost thread work > (TBD) is integrated and then vhost will actually be using its polling > cycles to handle requests of multiple devices (even from multiple vms). > > Thanks, > Razya -- MST -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
Christian Borntraeger wrote on 20/08/2014 11:41:32 AM: > > > > Results: > > > > Netperf, 1 vm: > > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 MB/sec). > > Number of exits/sec decreased 6x. > > The same improvement was shown when I tested with 3 vms running netperf > > (4086 MB/sec -> 5545 MB/sec). > > > > filebench, 1 vm: > > ops/sec improved by 13% with the polling patch. Number of exits > was reduced by > > 31%. > > The same experiment with 3 vms running filebench showed similar numbers. > > > > Signed-off-by: Razya Ladelsky > > Gave it a quick try on s390/kvm. As expected it makes no difference > for big streaming workload like iperf. > uperf with a 1-1 round robin got indeed faster by about 30%. > The high CPU consumption is something that bothers me though, as > virtualized systems tend to be full. > > Thanks for confirming the results! The best way to use this patch would be along with a shared vhost thread for multiple devices/vms, as described in: http://domino.research.ibm.com/library/cyberdig.nsf/1e4115aea78b6e7c85256b360066f0d4/479e3578ed05bfac85257b4200427735!OpenDocument This work assumes having a dedicated I/O core where the vhost thread serves multiple vms, which makes the high cpu utilization less of a concern. > > +static int poll_start_rate = 0; > > +module_param(poll_start_rate, int, S_IRUGO|S_IWUSR); > > +MODULE_PARM_DESC(poll_start_rate, "Start continuous polling of > virtqueue when rate of events is at least this number per jiffy. If > 0, never start polling."); > > + > > +static int poll_stop_idle = 3*HZ; /* 3 seconds */ > > +module_param(poll_stop_idle, int, S_IRUGO|S_IWUSR); > > +MODULE_PARM_DESC(poll_stop_idle, "Stop continuous polling of > virtqueue after this many jiffies of no work."); > > This seems ridicoudly high. Even one jiffie is an eternity, so > setting it to 1 as a default would reduce the CPU overhead for most cases. > If we dont have a packet in one millisecond, we can surely go back > to the kick approach, I think. > > Christian > Good point, will reduce it and recheck. Thank you, Razya -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
"Michael S. Tsirkin" wrote on 20/08/2014 01:57:10 PM: > > Results: > > > > Netperf, 1 vm: > > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 MB/sec). > > Number of exits/sec decreased 6x. > > The same improvement was shown when I tested with 3 vms running netperf > > (4086 MB/sec -> 5545 MB/sec). > > > > filebench, 1 vm: > > ops/sec improved by 13% with the polling patch. Number of exits > was reduced by > > 31%. > > The same experiment with 3 vms running filebench showed similar numbers. > > > > Signed-off-by: Razya Ladelsky > > This really needs more thourough benchmarking report, including > system data. One good example for a related patch: > http://lwn.net/Articles/551179/ > though for virtualization, we need data about host as well, and if you > want to look at streaming benchmarks, you need to test different message > sizes and measure packet size. > Hi Michael, I have already tried running netperf with several message sizes: 64,128,256,512,600,800... But the results are inconsistent even in the baseline/unpatched configuration. For smaller msg sizes, I get consistent numbers. However, at some point, when I increase the msg size I get unstable results. For example, for a 512B msg, I get two scenarios: vm utilization 100%, vhost utilization 75%, throughput ~6300 vm utilization 80%, vhost utilization 13%, throughput ~9400 (line rate) I don't know why vhost is behaving that way for certain message sizes. Do you have any insight to why this is happening? Thank you, Razya -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
RE: [PATCH] vhost: Add polling mode
From: Razya Ladelsky > "Michael S. Tsirkin" wrote on 20/08/2014 01:57:10 PM: > > > > Results: > > > > > > Netperf, 1 vm: > > > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 > > > MB/sec). > > > Number of exits/sec decreased 6x. > > > The same improvement was shown when I tested with 3 vms running netperf > > > (4086 MB/sec -> 5545 MB/sec). > > > > > > filebench, 1 vm: > > > ops/sec improved by 13% with the polling patch. Number of exits > > > was reduced by 31%. > > > The same experiment with 3 vms running filebench showed similar numbers. > > > > > > Signed-off-by: Razya Ladelsky > > > > This really needs more thourough benchmarking report, including > > system data. One good example for a related patch: > > http://lwn.net/Articles/551179/ > > though for virtualization, we need data about host as well, and if you > > want to look at streaming benchmarks, you need to test different message > > sizes and measure packet size. > > > > Hi Michael, > I have already tried running netperf with several message sizes: > 64,128,256,512,600,800... > But the results are inconsistent even in the baseline/unpatched > configuration. > For smaller msg sizes, I get consistent numbers. However, at some point, > when I increase the msg size > I get unstable results. For example, for a 512B msg, I get two scenarios: > vm utilization 100%, vhost utilization 75%, throughput ~6300 > vm utilization 80%, vhost utilization 13%, throughput ~9400 (line rate) > > I don't know why vhost is behaving that way for certain message sizes. > Do you have any insight to why this is happening? Have you tried looking at the actual ethernet packet sizes. It may well jump between using small packets (the size of the writes) and full sized ones. If you are trying to measure ethernet packet 'cost' you need to use UDP. However that probably uses different code paths. David -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
>> >
>> > Results:
>> >
>> > Netperf, 1 vm:
>> > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046 MB/sec).
>> > Number of exits/sec decreased 6x.
>> > The same improvement was shown when I tested with 3 vms running netperf
>> > (4086 MB/sec -> 5545 MB/sec).
>> >
>> > filebench, 1 vm:
>> > ops/sec improved by 13% with the polling patch. Number of exits
>> was reduced by
>> > 31%.
>> > The same experiment with 3 vms running filebench showed similar numbers.
>> >
>> > Signed-off-by: Razya Ladelsky
>>
>> Gave it a quick try on s390/kvm. As expected it makes no difference
>> for big streaming workload like iperf.
>> uperf with a 1-1 round robin got indeed faster by about 30%.
>> The high CPU consumption is something that bothers me though, as
>> virtualized systems tend to be full.
>>
>>
>
>Thanks for confirming the results!
>The best way to use this patch would be along with a shared vhost thread
>for multiple
>devices/vms, as described in:
>http://domino.research.ibm.com/library/cyberdig.nsf/1e4115aea78b6e7c85256b360066f0d4/479e3578ed05bfac85257b4200427735!OpenDocument
>This work assumes having a dedicated I/O core where the vhost thread
>serves multiple vms, which
>makes the high cpu utilization less of a concern.
>
Hi, Razya, Shirley
I am going to test the combination of
"several (depends on total number of cpu on host, e.g., total_number * 1/3)
vhost threads server all VMs" and "vhost: add polling mode",
now I get the patch
"http://thread.gmane.org/gmane.comp.emulators.kvm.devel/88682/focus=88723";
posted by Shirley,
any update to this patch?
And, I want to make a bit change on this patch, create total_cpu_number *
1/N(N={3,4}) vhost threads instead of per-cpu vhost thread to server all VMs,
any ideas?
Thanks,
Zhang Haoyu
>
>
>> > +static int poll_start_rate = 0;
>> > +module_param(poll_start_rate, int, S_IRUGO|S_IWUSR);
>> > +MODULE_PARM_DESC(poll_start_rate, "Start continuous polling of
>> virtqueue when rate of events is at least this number per jiffy. If
>> 0, never start polling.");
>> > +
>> > +static int poll_stop_idle = 3*HZ; /* 3 seconds */
>> > +module_param(poll_stop_idle, int, S_IRUGO|S_IWUSR);
>> > +MODULE_PARM_DESC(poll_stop_idle, "Stop continuous polling of
>> virtqueue after this many jiffies of no work.");
>>
>> This seems ridicoudly high. Even one jiffie is an eternity, so
>> setting it to 1 as a default would reduce the CPU overhead for most cases.
>> If we dont have a packet in one millisecond, we can surely go back
>> to the kick approach, I think.
>>
>> Christian
>>
>
>Good point, will reduce it and recheck.
>Thank you,
>Razya
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] vhost: Add polling mode
>>> >
>>> > Results:
>>> >
>>> > Netperf, 1 vm:
>>> > The polling patch improved throughput by ~33% (1516 MB/sec -> 2046
>>> > MB/sec).
>>> > Number of exits/sec decreased 6x.
>>> > The same improvement was shown when I tested with 3 vms running netperf
>>> > (4086 MB/sec -> 5545 MB/sec).
>>> >
>>> > filebench, 1 vm:
>>> > ops/sec improved by 13% with the polling patch. Number of exits
>>> was reduced by
>>> > 31%.
>>> > The same experiment with 3 vms running filebench showed similar numbers.
>>> >
>>> > Signed-off-by: Razya Ladelsky
>>>
>>> Gave it a quick try on s390/kvm. As expected it makes no difference
>>> for big streaming workload like iperf.
>>> uperf with a 1-1 round robin got indeed faster by about 30%.
>>> The high CPU consumption is something that bothers me though, as
>>> virtualized systems tend to be full.
>>>
>>>
>>
>>Thanks for confirming the results!
>>The best way to use this patch would be along with a shared vhost thread
>>for multiple
>>devices/vms, as described in:
>>http://domino.research.ibm.com/library/cyberdig.nsf/1e4115aea78b6e7c85256b360066f0d4/479e3578ed05bfac85257b4200427735!OpenDocument
>>This work assumes having a dedicated I/O core where the vhost thread
>>serves multiple vms, which
>>makes the high cpu utilization less of a concern.
>>
>Hi, Razya, Shirley
>I am going to test the combination of
>"several (depends on total number of cpu on host, e.g., total_number * 1/3)
>vhost threads server all VMs" and "vhost: add polling mode",
>now I get the patch
>"http://thread.gmane.org/gmane.comp.emulators.kvm.devel/88682/focus=88723";
>posted by Shirley,
>any update to this patch?
>
>And, I want to make a bit change on this patch, create total_cpu_number *
>1/N(N={3,4}) vhost threads instead of per-cpu vhost thread to server all VMs,
Just like xen netback threads, whose number is equal to num_online_cpus on
Dom0,
but for kvm host, I think per-cpu vhost thread is too many.
>any ideas?
>
>Thanks,
>Zhang Haoyu
>>
>>
>>> > +static int poll_start_rate = 0;
>>> > +module_param(poll_start_rate, int, S_IRUGO|S_IWUSR);
>>> > +MODULE_PARM_DESC(poll_start_rate, "Start continuous polling of
>>> virtqueue when rate of events is at least this number per jiffy. If
>>> 0, never start polling.");
>>> > +
>>> > +static int poll_stop_idle = 3*HZ; /* 3 seconds */
>>> > +module_param(poll_stop_idle, int, S_IRUGO|S_IWUSR);
>>> > +MODULE_PARM_DESC(poll_stop_idle, "Stop continuous polling of
>>> virtqueue after this many jiffies of no work.");
>>>
>>> This seems ridicoudly high. Even one jiffie is an eternity, so
>>> setting it to 1 as a default would reduce the CPU overhead for most cases.
>>> If we dont have a packet in one millisecond, we can surely go back
>>> to the kick approach, I think.
>>>
>>> Christian
>>>
>>
>>Good point, will reduce it and recheck.
>>Thank you,
>>Razya
--
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RE: [PATCH] vhost: Add polling mode
David Laight wrote on 21/08/2014 05:29:41 PM: > From: David Laight > To: Razya Ladelsky/Haifa/IBM@IBMIL, "Michael S. Tsirkin" > Cc: "abel.gor...@gmail.com" , Alex Glikson/ > Haifa/IBM@IBMIL, Eran Raichstein/Haifa/IBM@IBMIL, Joel Nider/Haifa/ > IBM@IBMIL, "kvm@vger.kernel.org" , "linux- > ker...@vger.kernel.org" , > "net...@vger.kernel.org" , > "virtualizat...@lists.linux-foundation.org" > , Yossi Kuperman1/Haifa/IBM@IBMIL > Date: 21/08/2014 05:31 PM > Subject: RE: [PATCH] vhost: Add polling mode > > From: Razya Ladelsky > > "Michael S. Tsirkin" wrote on 20/08/2014 01:57:10 PM: > > > > > > Results: > > > > > > > > Netperf, 1 vm: > > > > The polling patch improved throughput by ~33% (1516 MB/sec -> > 2046 MB/sec). > > > > Number of exits/sec decreased 6x. > > > > The same improvement was shown when I tested with 3 vms running netperf > > > > (4086 MB/sec -> 5545 MB/sec). > > > > > > > > filebench, 1 vm: > > > > ops/sec improved by 13% with the polling patch. Number of exits > > > > was reduced by 31%. > > > > The same experiment with 3 vms running filebench showed similar numbers. > > > > > > > > Signed-off-by: Razya Ladelsky > > > > > > This really needs more thourough benchmarking report, including > > > system data. One good example for a related patch: > > > http://lwn.net/Articles/551179/ > > > though for virtualization, we need data about host as well, and if you > > > want to look at streaming benchmarks, you need to test different message > > > sizes and measure packet size. > > > > > > > Hi Michael, > > I have already tried running netperf with several message sizes: > > 64,128,256,512,600,800... > > But the results are inconsistent even in the baseline/unpatched > > configuration. > > For smaller msg sizes, I get consistent numbers. However, at some point, > > when I increase the msg size > > I get unstable results. For example, for a 512B msg, I get two scenarios: > > vm utilization 100%, vhost utilization 75%, throughput ~6300 > > vm utilization 80%, vhost utilization 13%, throughput ~9400 (line rate) > > > > I don't know why vhost is behaving that way for certain message sizes. > > Do you have any insight to why this is happening? > > Have you tried looking at the actual ethernet packet sizes. > It may well jump between using small packets (the size of the writes) > and full sized ones. I will check it, Thanks, Razya > > If you are trying to measure ethernet packet 'cost' you need to use UDP. > However that probably uses different code paths. > >David > > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
