Hi all, I'm wondering why vhost-user dequeue zero-copy is removed. Could you please help me understand this question or let me know where I can find the discussions about this question?
Best Regards, Xu, Chenjie -----Original Message----- From: dev <ovs-dev-boun...@openvswitch.org> On Behalf Of Ian Stokes Sent: Tuesday, September 8, 2020 11:27 PM To: d...@openvswitch.org Cc: maxime.coque...@redhat.com; i.maxim...@ovn.org Subject: [ovs-dev] [PATCH v1 1/1] DPDK: Remove support for vhost-user zero-copy. Support for vhost-user dequeue zero-copy was deprecated in OVS 2.14 with the aim of removing it for OVS 2.15. Support for zero-copy will also be removed from DPDK 20.11. As such remove support from OVS. Signed-off-by: Ian Stokes <ian.sto...@intel.com> --- Documentation/topics/dpdk/vhost-user.rst | 72 -------------------------------- NEWS | 2 + lib/netdev-dpdk.c | 25 ----------- vswitchd/vswitch.xml | 11 ----- 4 files changed, 2 insertions(+), 108 deletions(-) diff --git a/Documentation/topics/dpdk/vhost-user.rst b/Documentation/topics/dpdk/vhost-user.rst index 4af738d11..595e40cde 100644 --- a/Documentation/topics/dpdk/vhost-user.rst +++ b/Documentation/topics/dpdk/vhost-user.rst @@ -553,78 +553,6 @@ shown with:: $ ovs-vsctl get Interface dpdkvhostclient0 statistics:ovs_tx_retries -vhost-user Dequeue Zero Copy (experimental) -------------------------------------------- - -.. warning:: - - vhost-user Dequeue Zero Copy is deprecated in OVS and will be removed in - the next release. - -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'. - -.. note:: - - Post-copy Live Migration is not compatible with dequeue zero copy. - Further information can be found in the `DPDK documentation <https://doc.dpdk.org/guides-19.11/prog_guide/vhost_lib.html>`__ diff --git a/NEWS b/NEWS index 2f67d5047..2db246d1a 100644 --- a/NEWS +++ b/NEWS @@ -1,5 +1,7 @@ Post-v2.14.0 --------------------- + - DPDK: + * Deprecated vhost-user dequeue zero-copy support removed. v2.14.0 - 17 Aug 2020 diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c index 18c4adcc7..515ad612e 100644 --- a/lib/netdev-dpdk.c +++ b/lib/netdev-dpdk.c @@ -2032,12 +2032,6 @@ netdev_dpdk_vhost_client_set_config(struct netdev *netdev, if (!nullable_string_is_equal(path, dev->vhost_id)) { free(dev->vhost_id); dev->vhost_id = nullable_xstrdup(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); } } @@ -5028,7 +5022,6 @@ netdev_dpdk_vhost_client_reconfigure(struct netdev *netdev) int err; uint64_t vhost_flags = 0; uint64_t vhost_unsup_flags; - bool zc_enabled; ovs_mutex_lock(&dev->mutex); @@ -5054,19 +5047,6 @@ netdev_dpdk_vhost_client_reconfigure(struct netdev *netdev) vhost_flags |= RTE_VHOST_USER_POSTCOPY_SUPPORT; } - zc_enabled = dev->vhost_driver_flags - & RTE_VHOST_USER_DEQUEUE_ZERO_COPY; - /* Enable zero copy flag, if requested */ - if (zc_enabled) { - vhost_flags |= RTE_VHOST_USER_DEQUEUE_ZERO_COPY; - /* DPDK vHost library doesn't allow zero-copy with linear buffers. - * Hence disable Linear buffer. - */ - vhost_flags &= ~RTE_VHOST_USER_LINEARBUF_SUPPORT; - VLOG_WARN("Zero copy enabled, disabling linear buffer" - " check for vHost port %s", dev->up.name); - } - /* Enable External Buffers if TCP Segmentation Offload is enabled. */ if (userspace_tso_enabled()) { vhost_flags |= RTE_VHOST_USER_EXTBUF_SUPPORT; @@ -5083,11 +5063,6 @@ 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 (zc_enabled) { - VLOG_INFO("Zero copy enabled for vHost port %s", dev->up.name); - VLOG_WARN("Zero copy support is deprecated and will be " - "removed in the next OVS release."); - } } err = rte_vhost_driver_callback_register(dev->vhost_id, diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml index 81c84927f..07da2ee8c 100644 --- a/vswitchd/vswitch.xml +++ b/vswitchd/vswitch.xml @@ -3236,17 +3236,6 @@ 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="tx-retries-max" type='{"type": "integer", "minInteger": 0, "maxInteger": 32}'> <p> -- 2.13.6 _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev
