Message bounced, I use new Denis's email address.
On Wed, Sep 08, 2021 at 03:17:16PM +0200, Stefano Garzarella wrote:
Hi Denis,
I just found this discussion since we still have the following line in
hw/core/machine.c:
{ "vhost-blk-device", "seg_max_adjust", "off"}
IIUC it was a typo, and I think we should fix it since in the future
we can have `vhost-blk-device`.
So, I think we have 2 options:
1. remove that line since for now is useless
2. replace with "vhost-scsi"
I'm not sure which is the best, what do you suggest?
Thanks,
Stefano
On Fri, Feb 07, 2020 at 11:48:05AM +0300, Denis Plotnikov wrote:
On 05.02.2020 14:19, Stefan Hajnoczi wrote:
On Tue, Feb 04, 2020 at 12:59:04PM +0300, Denis Plotnikov wrote:
On 30.01.2020 17:58, Stefan Hajnoczi wrote:
On Wed, Jan 29, 2020 at 05:07:00PM +0300, Denis Plotnikov wrote:
The goal is to reduce the amount of requests issued by a guest on
1M reads/writes. This rises the performance up to 4% on that kind of
disk access pattern.
The maximum chunk size to be used for the guest disk accessing is
limited with seg_max parameter, which represents the max amount of
pices in the scatter-geather list in one guest disk request.
Since seg_max is virqueue_size dependent, increasing the virtqueue
size increases seg_max, which, in turn, increases the maximum size
of data to be read/write from guest disk.
More details in the original problem statment:
https://lists.gnu.org/archive/html/qemu-devel/2017-12/msg03721.html
Suggested-by: Denis V. Lunev <d...@openvz.org>
Signed-off-by: Denis Plotnikov <dplotni...@virtuozzo.com>
---
hw/core/machine.c | 3 +++
include/hw/virtio/virtio.h | 2 +-
2 files changed, 4 insertions(+), 1 deletion(-)
diff --git a/hw/core/machine.c b/hw/core/machine.c
index 3e288bfceb..8bc401d8b7 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -28,6 +28,9 @@
#include "hw/mem/nvdimm.h"
GlobalProperty hw_compat_4_2[] = {
+ { "virtio-blk-device", "queue-size", "128"},
+ { "virtio-scsi-device", "virtqueue_size", "128"},
+ { "vhost-blk-device", "virtqueue_size", "128"},
vhost-blk-device?! Who has this? It's not in qemu.git so please omit
this line. ;-)
So in this case the line:
{ "vhost-blk-device", "seg_max_adjust", "off"},
introduced by my patch:
commit 1bf8a989a566b2ba41c197004ec2a02562a766a4
Author: Denis Plotnikov <dplotni...@virtuozzo.com>
Date: Fri Dec 20 17:09:04 2019 +0300
virtio: make seg_max virtqueue size dependent
is also wrong. It should be:
{ "vhost-scsi-device", "seg_max_adjust", "off"},
Am I right?
It's just called "vhost-scsi":
include/hw/virtio/vhost-scsi.h:#define TYPE_VHOST_SCSI "vhost-scsi"
On the other hand, do you want to do this for the vhost-user-blk,
vhost-user-scsi, and vhost-scsi devices that exist in qemu.git? Those
devices would benefit from better performance too.
After thinking about that for a while, I think we shouldn't extend
queue sizes for vhost-user-blk, vhost-user-scsi and vhost-scsi.
This is because increasing the queue sizes seems to be just useless
for them: the all thing is about increasing the queue sizes for
increasing seg_max (it limits the max block query size from the
guest). For virtio-blk-device and virtio-scsi-device it makes sense,
since they have seg-max-adjust property which, if true, sets seg_max
to virtqueue_size-2. vhost-scsi also have this property but it seems
the property just doesn't affect anything (remove it?).
Also vhost-user-blk, vhost-user-scsi and vhost-scsi don't do any
seg_max settings. If I understand correctly, their backends are ment
to be responsible for doing that.
So, what about changing the queue sizes just for virtio-blk-device
and virtio-scsi-device?
Denis
It seems to be so. We also have the test checking those settings:
tests/acceptance/virtio_seg_max_adjust.py
For now it checks virtio-scsi-pci and virtio-blk-pci.
I'm going to extend it for the virtqueue size checking.
If I change vhost-user-blk, vhost-user-scsi and vhost-scsi it's worth
to check those devices too. But I don't know how to form a command line
for that 3 devices since they should involve some third party components as
backends (kernel modules, DPDK, etc.) and they seems to be not available in
the
qemu git.
Is there any way to do it with some qit.qemu available stubs or something
else?
If so, could you please point out the proper way to do it?
qemu.git has contrib/vhost-user-blk/ and contrib/vhost-user-scsi/ if
you need to test those vhost-user devices without external dependencies.
Stefan
