From 9dcf5d15569b3c4f299dc5f903cda53f995bb158 Mon Sep 17 00:00:00 2001 From: Yinan Wang Date: Thu, 28 Nov 2019 15:30:21 +0100 Subject: [PATCH] doc: clarify path selection in virtio guide Add virtio paths selection and usage introduction for better virtio usability. Signed-off-by: Yinan Wang Acked-by: Tiwei Bie Reviewed-by: Maxime Coquelin --- doc/guides/nics/virtio.rst | 124 +++++++++++++++++++++++++++++++++++++ 1 file changed, 124 insertions(+) diff --git a/doc/guides/nics/virtio.rst b/doc/guides/nics/virtio.rst index fb378a4b94..d1f5fb8986 100644 --- a/doc/guides/nics/virtio.rst +++ b/doc/guides/nics/virtio.rst @@ -402,3 +402,127 @@ Below devargs are supported by the virtio-user vdev: It is used to enable virtio device packed virtqueue feature. (Default: 0 (disabled)) + +Virtio paths Selection and Usage +-------------------------------- + +Logically virtio-PMD has 9 paths based on the combination of virtio features +(Rx mergeable, In-order, Packed virtqueue), below is an introduction of these +features: + +* `Rx mergeable `_: With this feature negotiated, device + can receive large packets by combining individual descriptors. +* `In-order `_: Some devices always use descriptors + in the same order in which they have been made available, these + devices can offer the VIRTIO_F_IN_ORDER feature. With this feature negotiated, + driver will use descriptors in order. +* `Packed virtqueue `_: The structure of packed virtqueue is + different from split virtqueue, split virtqueue is composed of available ring, + used ring and descriptor table, while packed virtqueue is composed of descriptor + ring, driver event suppression and device event suppression. The idea behind + this is to improve performance by avoiding cache misses and make it easier + for hardware to implement. + +Virtio paths Selection +~~~~~~~~~~~~~~~~~~~~~~ + +If packed virtqueue is not negotiated, below split virtqueue paths will be selected +according to below configuration: + +#. Split virtqueue mergeable path: If Rx mergeable is negotiated, in-order feature is + not negotiated, this path will be selected. +#. Split virtqueue non-mergeable path: If Rx mergeable and in-order feature are not + negotiated, also Rx offload(s) are requested, this path will be selected. +#. Split virtqueue in-order mergeable path: If Rx mergeable and in-order feature are + both negotiated, this path will be selected. +#. Split virtqueue in-order non-mergeable path: If in-order feature is negotiated and + Rx mergeable is not negotiated, this path will be selected. +#. Split virtqueue vectorized Rx path: If Rx mergeable is disabled and no Rx offload + requested, this path will be selected. + +If packed virtqueue is negotiated, below packed virtqueue paths will be selected +according to below configuration: + +#. Packed virtqueue mergeable path: If Rx mergeable is negotiated, in-order feature + is not negotiated, this path will be selected. +#. Packed virtqueue non-mergeable path: If Rx mergeable and in-order feature are not + negotiated, this path will be selected. +#. Packed virtqueue in-order mergeable path: If in-order and Rx mergeable feature are + both negotiated, this path will be selected. +#. Packed virtqueue in-order non-mergeable path: If in-order feature is negotiated and + Rx mergeable is not negotiated, this path will be selected. + +Rx/Tx callbacks of each Virtio path +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Refer to above description, virtio path and corresponding Rx/Tx callbacks will +be selected automatically. Rx callbacks and Tx callbacks for each virtio path +are shown in below table: + +.. table:: Virtio Paths and Callbacks + + ============================================ ================================= ======================== + Virtio paths Rx callbacks Tx callbacks + ============================================ ================================= ======================== + Split virtqueue mergeable path virtio_recv_mergeable_pkts virtio_xmit_pkts + Split virtqueue non-mergeable path virtio_recv_pkts virtio_xmit_pkts + Split virtqueue in-order mergeable path virtio_recv_pkts_inorder virtio_xmit_pkts_inorder + Split virtqueue in-order non-mergeable path virtio_recv_pkts_inorder virtio_xmit_pkts_inorder + Split virtqueue vectorized Rx path virtio_recv_pkts_vec virtio_xmit_pkts + Packed virtqueue mergeable path virtio_recv_mergeable_pkts_packed virtio_xmit_pkts_packed + Packed virtqueue non-meregable path virtio_recv_pkts_packed virtio_xmit_pkts_packed + Packed virtqueue in-order mergeable path virtio_recv_mergeable_pkts_packed virtio_xmit_pkts_packed + Packed virtqueue in-order non-mergeable path virtio_recv_pkts_packed virtio_xmit_pkts_packed + ============================================ ================================= ======================== + +Virtio paths Support Status from Release to Release +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Virtio feature implementation: + +* In-order feature is supported since DPDK 18.08 by adding new Rx/Tx callbacks + ``virtio_recv_pkts_inorder`` and ``virtio_xmit_pkts_inorder``. +* Packed virtqueue is supported since DPDK 19.02 by adding new Rx/Tx callbacks + ``virtio_recv_pkts_packed`` , ``virtio_recv_mergeable_pkts_packed`` and + ``virtio_xmit_pkts_packed``. + +All virtio paths support status are shown in below table: + +.. table:: Virtio Paths and Releases + + ============================================ ============= ============= ============= + Virtio paths 16.11 ~ 18.05 18.08 ~ 18.11 19.02 ~ 19.11 + ============================================ ============= ============= ============= + Split virtqueue mergeable path Y Y Y + Split virtqueue non-mergeable path Y Y Y + Split virtqueue vectorized Rx path Y Y Y + Split virtqueue simple Tx path Y N N + Split virtqueue in-order mergeable path Y Y + Split virtqueue in-order non-mergeable path Y Y + Packed virtqueue mergeable path Y + Packed virtqueue non-mergeable path Y + Packed virtqueue in-order mergeable path Y + Packed virtqueue in-order non-mergeable path Y + ============================================ ============= ============= ============= + +QEMU Support Status +~~~~~~~~~~~~~~~~~~~ + +* Qemu now supports three paths of split virtqueue: Split virtqueue mergeable path, + Split virtqueue non-mergeable path, Split virtqueue vectorized Rx path. +* Since qemu 4.2.0, Packed virtqueue mergeable path and Packed virtqueue non-mergeable + path can be supported. + +How to Debug +~~~~~~~~~~~~ + +If you meet performance drop or some other issues after upgrading the driver +or configuration, below steps can help you identify which path you selected and +root cause faster. + +#. Run vhost/virtio test case; +#. Run "perf top" and check virtio Rx/Tx callback names; +#. Identify which virtio path is selected refer to above table. -- 2.20.1