>
> On 19.01.2018 20:19, 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 <[email protected]>
> > ---
> > v9:
> > * Rebase
> > * Fix docs issue
> > * Move variable asignment inside mutex
> > * Reset dq-zero-copy value if vhost_driver_register fails
> >
> > Documentation/intro/install/dpdk.rst | 2 +
> > Documentation/topics/dpdk/vhost-user.rst | 73
> ++++++++++++++++++++++++++++++++
> > NEWS | 1 +
> > lib/netdev-dpdk.c | 11 ++++-
> > vswitchd/vswitch.xml | 11 +++++
> > 5 files changed, 97 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..95517a6 100644
> > --- a/Documentation/topics/dpdk/vhost-user.rst
> > +++ b/Documentation/topics/dpdk/vhost-user.rst
> > @@ -458,3 +458,76 @@ 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-queues-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 considered '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>`__
> > diff --git a/NEWS b/NEWS
> > index c067b94..51f9e04 100644
> > --- a/NEWS
> > +++ b/NEWS
> > @@ -47,6 +47,7 @@ v2.9.0 - xx xxx xxxx
> > "management" statistics.
> > - ovs-ofctl dump-ports command now prints new of set custom
> statistics
> > if available (for OpenFlow 1.4+).
> > + * Add support for vHost dequeue zero copy (experimental)
> > - vswitchd:
> > * Datapath IDs may now be specified as 0x1 (etc.) instead of 16
> > digits.
> > * Configuring a controller, or unconfiguring all controllers, now
> > deletes
> > diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c
> > index e32c7f6..8111eba 100644
> > --- a/lib/netdev-dpdk.c
> > +++ b/lib/netdev-dpdk.c
> > @@ -1519,6 +1519,12 @@ 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;
> > + } else {
> > + dev->vhost_driver_flags &=
> ~RTE_VHOST_USER_DEQUEUE_ZERO_COPY;
> > + }
> > netdev_request_reconfigure(netdev);
> > }
> > }
> > @@ -3521,7 +3527,7 @@ netdev_dpdk_vhost_client_reconfigure(struct
> netdev *netdev)
> > if (!(dev->vhost_driver_flags & RTE_VHOST_USER_CLIENT)
> > && strlen(dev->vhost_id)) {
> > /* Register client-mode device. */
> > - vhost_flags |= RTE_VHOST_USER_CLIENT;
> > + vhost_flags = dev->vhost_driver_flags |= RTE_VHOST_USER_CLIENT;
>
> RTE_VHOST_USER_CLIENT should be enabled in dev->vhost_driver_flags
> only
> after successful driver regirter. Otherwise we'll not be able to do anything
> with this device in case of failure.
Thanks for the catch Ilya. I think removing the = could suffice, but I've
expanded it a bit in the new patch to make it more obvious and readable.
Thanks,
Ciara
>
> >
> > /* Enable IOMMU support, if explicitly requested. */
> > if (dpdk_vhost_iommu_enabled()) {
> > @@ -3538,6 +3544,9 @@ 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 58c0ebd..0e47c14 100644
> > --- a/vswitchd/vswitch.xml
> > +++ b/vswitchd/vswitch.xml
> > @@ -2671,6 +2671,17 @@ 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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