Enabled per port like so: ovs-vsctl set Interface dpdkvhostuserclient0 options:dq-zero-copy=true
The feature is disabled by default and can only be enabled/disabled when a vHost port is down. When packets from a vHost device with zero copy enabled are destined for a '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 Due to the requirement above, the feature is considered 'experimental'. Signed-off-by: Ciara Loftus <[email protected]> --- v6: * Note the feature is experimental. * Mention bug in DPDK & temporary requirement on QEMU < v2.7 Documentation/howto/dpdk.rst | 33 ++++++++++++ Documentation/topics/dpdk/vhost-user.rst | 68 ++++++++++++++++++++++++ NEWS | 2 + lib/netdev-dpdk.c | 89 +++++++++++++++++++++++++++++++- vswitchd/vswitch.xml | 11 ++++ 5 files changed, 202 insertions(+), 1 deletion(-) diff --git a/Documentation/howto/dpdk.rst b/Documentation/howto/dpdk.rst index d123819..3e1b8f8 100644 --- a/Documentation/howto/dpdk.rst +++ b/Documentation/howto/dpdk.rst @@ -709,3 +709,36 @@ devices to bridge ``br0``. Once complete, follow the below steps: Check traffic on multiple queues:: $ cat /proc/interrupts | grep virtio + +PHY-VM-PHY (vHost Dequeue Zero Copy) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +vHost dequeue zero copy functionality can be validated using the +PHY-VM-PHY configuration. To begin, follow the steps described in +:ref:`dpdk-phy-phy` to create and initialize the database, start +ovs-vswitchd and add ``dpdk``-type and ``dpdkvhostuser``-type devices +and flows to bridge ``br0``. Once complete, follow the below steps: + +1. Enable dequeue zero copy on the vHost devices. + + $ ovs-vsctl set Interface dpdkvhostuser0 options:dq-zero-copy=true + $ ovs-vsctl set Interface dpdkvhostuser1 options:dq-zero-copy=true + +The following log should be observed for each device: + + netdev_dpdk|INFO|Zero copy enabled for vHost socket <name> + +2. Reduce the number of txq descriptors on the phy ports. + + $ ovs-vsctl set Interface phy0 options:n_txq_desc=128 + $ ovs-vsctl set Interface phy1 options:n_txq_desc=128 + +3. Proceed with the test by launching the VM and configuring guest +forwarding, be it via the vHost loopback method or kernel forwarding +method, and sending traffic. The following log should be oberved for +each device as it becomes active during VM boot: + + VHOST_CONFIG: dequeue zero copy is enabled + +It is essential that step 1 is performed before booting the VM, otherwise +the feature will not be enabled. diff --git a/Documentation/topics/dpdk/vhost-user.rst b/Documentation/topics/dpdk/vhost-user.rst index 8447e2d..5a65360 100644 --- a/Documentation/topics/dpdk/vhost-user.rst +++ b/Documentation/topics/dpdk/vhost-user.rst @@ -458,3 +458,71 @@ 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 set Interface dpdkvhostuserclient0 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 using the command above. + +The feature cannot be enabled when the device is active (ie. VM booted). If +you wish to enable the feature after the VM has booted, you must shutdown +the VM and bring it back up. + +The same logic applies for disabling the feature - it must be disabled when +the device is inactive, for example before VM boot. To disable the feature: + + $ ovs-vsctl set Interface dpdkvhostuserclient0 options:dq-zero-copy=false + +The feature is available to both dpdkvhostuser and 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 + +More information on the n_txq_desc option can be found in the "DPDK Physical +Port Queue Sizes" section of the `intro/install/dpdk.rst` guide. + +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 here: +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 49d2fa5..5921b50 100644 --- a/NEWS +++ b/NEWS @@ -23,6 +23,8 @@ Post-v2.8.0 - DPDK: * Add support for DPDK v17.11 * Add support for vHost IOMMU + * Optional dequeue zero copy feature for vHost ports (experimental) can be + enabled per port via the boolean 'dq-zero-copy' option. v2.8.0 - 31 Aug 2017 -------------------- diff --git a/lib/netdev-dpdk.c b/lib/netdev-dpdk.c index 5068d4e..b52e993 100644 --- a/lib/netdev-dpdk.c +++ b/lib/netdev-dpdk.c @@ -379,6 +379,9 @@ struct netdev_dpdk { /* True if vHost device is 'up' and has been reconfigured at least once */ bool vhost_reconfigured; /* 3 pad bytes here. */ + + /* True if dq-zero-copy feature has successfully been enabled */ + bool dq_zc_enabled; ); PADDED_MEMBERS(CACHE_LINE_SIZE, @@ -889,6 +892,7 @@ common_construct(struct netdev *netdev, dpdk_port_t port_no, dev->max_packet_len = MTU_TO_FRAME_LEN(dev->mtu); ovsrcu_index_init(&dev->vid, -1); dev->vhost_reconfigured = false; + dev->dq_zc_enabled = false; dev->attached = false; ovsrcu_init(&dev->qos_conf, NULL); @@ -1400,6 +1404,29 @@ netdev_dpdk_ring_set_config(struct netdev *netdev, const struct smap *args, return 0; } +static void +dpdk_vhost_set_config_helper(struct netdev_dpdk *dev, + const struct smap *args) +{ + bool needs_reconfigure = false; + bool zc_requested = smap_get_bool(args, "dq-zero-copy", false); + + if (zc_requested && + !(dev->vhost_driver_flags & RTE_VHOST_USER_DEQUEUE_ZERO_COPY)) { + dev->vhost_driver_flags |= RTE_VHOST_USER_DEQUEUE_ZERO_COPY; + needs_reconfigure = true; + } else if (!zc_requested && + (dev->vhost_driver_flags & RTE_VHOST_USER_DEQUEUE_ZERO_COPY)) { + dev->vhost_driver_flags &= ~RTE_VHOST_USER_DEQUEUE_ZERO_COPY; + needs_reconfigure = true; + } + + /* Only try to change ZC mode when device is down */ + if (needs_reconfigure && (netdev_dpdk_get_vid(dev) == -1)) { + netdev_request_reconfigure(&dev->up); + } +} + static int netdev_dpdk_vhost_client_set_config(struct netdev *netdev, const struct smap *args, @@ -1416,6 +1443,23 @@ netdev_dpdk_vhost_client_set_config(struct netdev *netdev, netdev_request_reconfigure(netdev); } } + + dpdk_vhost_set_config_helper(dev, args); + + ovs_mutex_unlock(&dev->mutex); + + return 0; +} + +static int +netdev_dpdk_vhost_set_config(struct netdev *netdev, + const struct smap *args, + char **errp OVS_UNUSED) +{ + struct netdev_dpdk *dev = netdev_dpdk_cast(netdev); + + ovs_mutex_lock(&dev->mutex); + dpdk_vhost_set_config_helper(dev, args); ovs_mutex_unlock(&dev->mutex); return 0; @@ -2748,6 +2792,46 @@ netdev_dpdk_txq_map_clear(struct netdev_dpdk *dev) } } +static void +vhost_change_zero_copy_mode(struct netdev_dpdk *dev, bool client_mode, + bool enable) +{ + int err = rte_vhost_driver_unregister(dev->vhost_id); + + if (err) { + VLOG_ERR("Error unregistering vHost socket %s; can't change zero copy " + "mode", dev->vhost_id); + } else { + err = dpdk_setup_vhost_device(dev, client_mode); + if (err) { + VLOG_ERR("Error changing zero copy mode for vHost socket %s", + dev->vhost_id); + } else if (enable) { + dev->dq_zc_enabled = true; + VLOG_INFO("Zero copy enabled for vHost socket %s", dev->vhost_id); + } else { + dev->dq_zc_enabled = false; + VLOG_INFO("Zero copy disabled for vHost socket %s", dev->vhost_id); + } + } +} + +static void +vhost_check_zero_copy_status(struct netdev_dpdk *dev) +{ + bool mode = dev->vhost_driver_flags & RTE_VHOST_USER_CLIENT; + + if ((dev->vhost_driver_flags & RTE_VHOST_USER_DEQUEUE_ZERO_COPY) + && !dev->dq_zc_enabled) { + /* ZC disabled but requested to be enabled, enable it. */ + vhost_change_zero_copy_mode(dev, mode, true); + } else if (!(dev->vhost_driver_flags & + RTE_VHOST_USER_DEQUEUE_ZERO_COPY) && dev->dq_zc_enabled) { + /* ZC enabled but requested to be disabled, disable it. */ + vhost_change_zero_copy_mode(dev, mode, false); + } +} + /* * Remove a virtio-net device from the specific vhost port. Use dev->remove * flag to stop any more packets from being sent or received to/from a VM and @@ -2793,6 +2877,7 @@ destroy_device(int vid) */ ovsrcu_quiesce_start(); VLOG_INFO("vHost Device '%s' has been removed", ifname); + netdev_request_reconfigure(&dev->up); } else { VLOG_INFO("vHost Device '%s' not found", ifname); } @@ -3284,6 +3369,8 @@ dpdk_vhost_reconfigure_helper(struct netdev_dpdk *dev) /* Carrier status may need updating. */ netdev_change_seq_changed(&dev->up); } + } else { + vhost_check_zero_copy_status(dev); } return 0; @@ -3446,7 +3533,7 @@ static const struct netdev_class dpdk_vhost_class = NULL, netdev_dpdk_vhost_construct, netdev_dpdk_vhost_destruct, - NULL, + netdev_dpdk_vhost_set_config, NULL, netdev_dpdk_vhost_send, netdev_dpdk_vhost_get_carrier, diff --git a/vswitchd/vswitch.xml b/vswitchd/vswitch.xml index 21ffaf5..330b028 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. The feature is considered experimental. + The port must be in an inactive state in order to enable or disable + this feature. + Only supported by dpdkvhostuserclient and dpdkvhostuser interfaces. + </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
