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 <ciara.lof...@intel.com> > --- > 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. > > /* 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> > _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev