> -----Original Message----- > From: Loftus, Ciara > Sent: Friday, January 5, 2018 4:14 PM > To: [email protected] > Cc: Loftus, Ciara <[email protected]>; Stokes, Ian > <[email protected]>; [email protected]; [email protected]; > [email protected] > Subject: [PATCH v8] netdev-dpdk: Add support for vHost dequeue zero copy > (experimental) >
Hi Ciara, This seems to have been simplified from the previous patchsets, I'll need to do some testing but some comments inline below that could be addressed for a v9. Thanks Ian > 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]> > --- > 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. Compilation fails with the following from above during the Doc check stage: WARNING: undefined label: <dpdk-queue-sizes> (if the link has no caption the label must precede a section header) > + > +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'. Minor: typo above for 'considered'. > + > +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 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; > + } > 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; > > 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> > -- > 2.7.5 _______________________________________________ dev mailing list [email protected] https://mail.openvswitch.org/mailman/listinfo/ovs-dev
