>
> On 05.01.2018 19:13, Ciara Loftus wrote:
> > Zero copy is disabled by default. To enable it, set the 'dq-zero-copy'
> > option to 'true' when configuring the Interface:
> >
> > ovs-vsctl set Interface dpdkvhostuserclient0
> > options:vhost-server-path=/tmp/dpdkvhostuserclient0
> > options:dq-zero-copy=true
> >
> > When packets from a vHost device with zero copy enabled are destined for
> > a single 'dpdk' port, the number of tx descriptors on that 'dpdk' port
> > must be set to a smaller value. 128 is recommended. This can be achieved
> > like so:
> >
> > ovs-vsctl set Interface dpdkport options:n_txq_desc=128
> >
> > Note: The sum of the tx descriptors of all 'dpdk' ports the VM will send
> > to should not exceed 128. Due to this requirement, the feature is
> > considered 'experimental'.
> >
> > Testing of the patch showed a 15% improvement when switching 512B
> > packets between vHost devices on different VMs on the same host when
> > zero copy was enabled on the transmitting device.
> >
> > Signed-off-by: Ciara Loftus <ciara.lof...@intel.com>
> > ---
> > v8:
> > * Disallow configurability after vHost device has been registered &
> > update docs accordingly.
> > * Give performance datapoint in commit message.
> >
> > Documentation/intro/install/dpdk.rst | 2 +
> > Documentation/topics/dpdk/vhost-user.rst | 72
> ++++++++++++++++++++++++++++++++
> > NEWS | 1 +
> > lib/netdev-dpdk.c | 9 +++-
> > vswitchd/vswitch.xml | 11 +++++
> > 5 files changed, 94 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/intro/install/dpdk.rst
> b/Documentation/intro/install/dpdk.rst
> > index 3fecb5c..087eb88 100644
> > --- a/Documentation/intro/install/dpdk.rst
> > +++ b/Documentation/intro/install/dpdk.rst
> > @@ -518,6 +518,8 @@ The above command sets the number of rx queues
> for DPDK physical interface.
> > The rx queues are assigned to pmd threads on the same NUMA node in a
> > round-robin fashion.
> >
> > +.. _dpdk-queues-sizes:
> > +
> > DPDK Physical Port Queue Sizes
> > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > diff --git a/Documentation/topics/dpdk/vhost-user.rst
> b/Documentation/topics/dpdk/vhost-user.rst
> > index 8447e2d..1a6c6d0 100644
> > --- a/Documentation/topics/dpdk/vhost-user.rst
> > +++ b/Documentation/topics/dpdk/vhost-user.rst
> > @@ -458,3 +458,75 @@ Sample XML
> > </domain>
> >
> > .. _QEMU documentation: http://git.qemu-
> project.org/?p=qemu.git;a=blob;f=docs/specs/vhost-
> user.txt;h=7890d7169;hb=HEAD
> > +
> > +vhost-user Dequeue Zero Copy (experimental)
> > +-------------------------------------------
> > +
> > +Normally when dequeuing a packet from a vHost User device, a memcpy
> operation
> > +must be used to copy that packet from guest address space to host
> address
> > +space. This memcpy can be removed by enabling dequeue zero-copy like
> so::
> > +
> > + $ ovs-vsctl add-port br0 dpdkvhostuserclient0 -- set Interface \
> > + dpdkvhostuserclient0 type=dpdkvhostuserclient \
> > + options:vhost-server-path=/tmp/dpdkvhostclient0 \
> > + options:dq-zero-copy=true
> > +
> > +With this feature enabled, a reference (pointer) to the packet is passed to
> > +the host, instead of a copy of the packet. Removing this memcpy can give
> a
> > +performance improvement for some use cases, for example switching
> large packets
> > +between different VMs. However additional packet loss may be
> observed.
> > +
> > +Note that the feature is disabled by default and must be explicitly enabled
> > +by setting the 'dq-zero-copy' option to 'true' while specifying the
> > +'vhost-server-path' option as above. If you wish to split out the command
> into
> > +multiple commands as below, ensure 'dq-zero-copy' is set before
> > +'vhost-server-path'::
> > +
> > + $ ovs-vsctl set Interface dpdkvhostuserclient0 options:dq-zero-
> copy=true
> > + $ ovs-vsctl set Interface dpdkvhostuserclient0 \
> > + options:vhost-server-path=/tmp/dpdkvhostclient0
> > +
> > +The feature is only available to dpdkvhostuserclient port types.
> > +
> > +A limitation exists whereby if packets from a vHost port with dq-zero-
> copy=true
> > +are destined for a 'dpdk' type port, the number of tx descriptors
> (n_txq_desc)
> > +for that port must be reduced to a smaller number, 128 being the
> recommended
> > +value. This can be achieved by issuing the following command::
> > +
> > + $ ovs-vsctl set Interface dpdkport options:n_txq_desc=128
> > +
> > +Note: The sum of the tx descriptors of all 'dpdk' ports the VM will send to
> > +should not exceed 128. For example, in case of a bond over two physical
> ports
> > +in balance-tcp mode, one must divide 128 by the number of links in the
> bond.
> > +
> > +Refer to :ref:`<dpdk-queue-sizes>` for more information.
> > +
> > +The reason for this limitation is due to how the zero copy functionality is
> > +implemented. The vHost device's 'tx used vring', a virtio structure used
> > for
> > +tracking used ie. sent descriptors, will only be updated when the NIC
> frees
> > +the corresponding mbuf. If we don't free the mbufs frequently enough,
> that
> > +vring will be starved and packets will no longer be processed. One way to
> > +ensure we don't encounter this scenario, is to configure n_txq_desc to a
> small
> > +enough number such that the 'mbuf free threshold' for the NIC will be hit
> more
> > +often and thus free mbufs more frequently. The value of 128 is
> suggested, but
> > +values of 64 and 256 have been tested and verified to work too, with
> differing
> > +performance characteristics. A value of 512 can be used too, if the virtio
> > +queue size in the guest is increased to 1024 (available to configure in
> QEMU
> > +versions v2.10 and greater). This value can be set like so::
> > +
> > + $ qemu-system-x86_64 ... -chardev
> socket,id=char1,path=<sockpath>,server
> > + -netdev type=vhost-user,id=mynet1,chardev=char1,vhostforce
> > + -device virtio-net-pci,mac=00:00:00:00:00:01,netdev=mynet1,
> > + tx_queue_size=1024
> > +
> > +Because of this limitation, this feature is condsidered 'experimental'.
> > +
> > +The feature currently does not fully work with QEMU >= v2.7 due to a bug
> in
> > +DPDK which will be addressed in an upcoming release. The patch to fix this
> > +issue can be found on
> > +`Patchwork
> > +<http://dpdk.org/dev/patchwork/patch/32198/>`__
> > +
> > +Further information can be found in the
> > +`DPDK documentation
> > +<http://dpdk.readthedocs.io/en/v17.05/prog_guide/vhost_lib.html>`__
>
> There are many keywords like 'vhost-server-path', 'dq-zero-copy', 'true' and
> so on in above text. IMHO, they should be marked like ``something`` to be
> highlighted.
>
> > diff --git a/NEWS b/NEWS
> > index 752e98f..1eaa32c 100644
> > --- a/NEWS
> > +++ b/NEWS
> > @@ -24,6 +24,7 @@ Post-v2.8.0
> > - DPDK:
> > * Add support for DPDK v17.11
> > * Add support for vHost IOMMU
> > + * Add support for vHost dequeue zero copy (experimental)
> >
> > v2.8.0 - 31 Aug 2017
> > --------------------
> > diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
> > index 8f22264..d100b31 100644
> > --- a/lib/netdev-dpdk.c
> > +++ b/lib/netdev-dpdk.c
> > @@ -1384,6 +1384,10 @@ netdev_dpdk_vhost_client_set_config(struct
> netdev *netdev,
> > path = smap_get(args, "vhost-server-path");
> > if (path && strcmp(path, dev->vhost_id)) {
> > strcpy(dev->vhost_id, path);
> > + /* check zero copy configuration */
> > + if (smap_get_bool(args, "dq-zero-copy", false)) {
> > + dev->vhost_driver_flags |=
> RTE_VHOST_USER_DEQUEUE_ZERO_COPY;
>
> In case of rte_vhost_driver_register() failure while reconfiguration we'll not
> be able to disable "dq-zero-copy" for that port, becose we're only anble to
> enable it.
> For example, it could happen in case of typo in vhost_id.
Hi Ilya,
Can you clarify what you want here. Previously we had the ability to
enable/disable zc but I removed it due to your comments.
Do you want to be able to enable/disable zc before successful driver register
but not after? What is the benefit?
Thanks,
Ciara
>
> > + }
> > netdev_request_reconfigure(netdev);
> > }
> > }
> > @@ -3278,7 +3282,7 @@ netdev_dpdk_vhost_client_reconfigure(struct
> netdev *netdev)
> > {
> > struct netdev_dpdk *dev = netdev_dpdk_cast(netdev);
> > int err;
> > - uint64_t vhost_flags = 0;
> > + uint64_t vhost_flags = dev->vhost_driver_flags;
>
> This should be under the mutex.
>
> >
> > ovs_mutex_lock(&dev->mutex);
> >
> > @@ -3307,6 +3311,9 @@ netdev_dpdk_vhost_client_reconfigure(struct
> netdev *netdev)
> > VLOG_INFO("vHost User device '%s' created in 'client' mode, "
> > "using client socket '%s'",
> > dev->up.name, dev->vhost_id);
> > + if (dev->vhost_driver_flags &
> RTE_VHOST_USER_DEQUEUE_ZERO_COPY) {
> > + VLOG_INFO("Zero copy enabled for vHost port %s", dev-
> >up.name);
> > + }
> > }
> >
> > err = rte_vhost_driver_callback_register(dev->vhost_id,
> > diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml
> > index 018d644..16b3c3e 100644
> > --- a/vswitchd/vswitch.xml
> > +++ b/vswitchd/vswitch.xml
> > @@ -2669,6 +2669,17 @@ ovs-vsctl add-port br0 p0 -- set Interface p0
> type=patch options:peer=p1 \
> > </p>
> > </column>
> >
> > + <column name="options" key="dq-zero-copy"
> > + type='{"type": "boolean"}'>
> > + <p>
> > + The value specifies whether or not to enable dequeue zero copy on
> > + the given interface.
> > + Must be set before vhost-server-path is specified.
> > + Only supported by dpdkvhostuserclient interfaces.
> > + The feature is considered experimental.
> > + </p>
> > + </column>
> > +
> > <column name="options" key="n_rxq_desc"
> > type='{"type": "integer", "minInteger": 1, "maxInteger":
> > 4096}'>
> > <p>
> >
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