Hi Yinan,
Thanks for the work! Will take a closer look ASAP. Please see some quick comments inline. On Tue, Nov 26, 2019 at 05:42:38AM -0500, Yinan wrote: > From: Wang Yinan <yinan.w...@intel.com> > > add virtio paths selection and usage introduction for better > virtio usability. > > Signed-off-by: Wang Yinan <yinan.w...@intel.com> > --- When sending new versions, please use --in-reply-to [1]. And it would be better if you can add a brief changelog. [1] https://core.dpdk.org/contribute/#send > doc/guides/howto/index.rst | 1 + > .../virtio_paths_selection_and_usage.rst | 142 ++++++++++++++++++ > 2 files changed, 143 insertions(+) > create mode 100644 doc/guides/howto/virtio_paths_selection_and_usage.rst > > diff --git a/doc/guides/howto/index.rst b/doc/guides/howto/index.rst > index a4c131652..6edb8d5be 100644 > --- a/doc/guides/howto/index.rst > +++ b/doc/guides/howto/index.rst > @@ -16,6 +16,7 @@ HowTo Guides > vfd > virtio_user_for_container_networking > virtio_user_as_exceptional_path > + virtio_paths_selection_and_usage > packet_capture_framework > telemetry > debug_troubleshoot > diff --git a/doc/guides/howto/virtio_paths_selection_and_usage.rst > b/doc/guides/howto/virtio_paths_selection_and_usage.rst > new file mode 100644 > index 000000000..bfd933fac > --- /dev/null > +++ b/doc/guides/howto/virtio_paths_selection_and_usage.rst > @@ -0,0 +1,142 @@ > +.. SPDX-License-Identifier: BSD-3-Clause > + Copyright(c) 2019 Intel Corporation. > + > +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 > virtio > +common features: > + > +* `Rx mergeable <https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/ > + virtio-v1.1-cs01.html#x1-700009>`_: With this feature negotiated, device Instead of referring to "Multi-buffer requests", below section is more related: https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/virtio-v1.1-cs01.html#x1-2140004 > + can receive larger packets by combining individual descriptors. > +* `In-order <https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/ > + virtio-v1.1-cs01.html#x1-690008>`_: 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. If this feature > negotiated, > + driver will use descriptors in order. Meanwhile, this knowledge allows > device > + operate used ring in batches and driver operate available ring in > batches and > + such can decrease cache miss rate. > +* `Packed virtqueue <https://docs.oasis-open.org/virtio/virtio/v1.1/cs01/ > + virtio-v1.1-cs01.html#x1-610007>`_: 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 and make it > easier > + for devices to implement. > + > +Virtio paths Selection > +---------------------- > + > +If packed virtqueue is not negotiated, below split virtqueue paths can 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 can be selected. s/can be/will be/ This applies to other similar cases as well. > +#. Split virtqueue in-order mergeable path: If in-order feature and Rx > mergeable are > + both negotiated, this path can be selected. > +#. Split virtqueue in-order non-mergeable path: If in-order feature is > negotiated and > + Rx mergeable is not negotiated, this path can be selected. > +#. Split virtqueue vectorized RX path: If Rx mergeable is disabled and no Rx > offload > + requested, this path can be selected. > + > +If packed virtqueue is negotiated, below packed virtqueue paths can 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, also Rx offload(s) are requested, this path will be selected. Currently, requesting Rx offload or not doesn't matter in this case. > +#. Packed virtqueue in-order mergeable path: If in-order feature and Rx > mergeable 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 descriptions, virtio path and Rx/TX callbacks are auto > selected by > +different parameters of vdev and workloads. Rx callbacks and Tx callbacks > name for > +each Virtio Path are shown in following tables:: > + > + > +----------------------------------------------------------------------------------------------------------+ > + | Virtio path | 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 normal 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 normal path | virtio_recv_pkts_packed > | virtio_xmit_pkts_packed | > + > +----------------------------------------------------------------------------------------------------------+ > + > +Virtio paths Support Status from Release to Release > +--------------------------------------------------- > + > +Virtio feature implementation: > + > +* In-order feature implemented in DPDK 18.08 by adding new Rx/TX callbacks > + ``virtio_recv_pkts_inorder`` and ``virtio_xmit_pkts_inorder``. > +* Packed virtqueue implemented in DPDK 19.02 by adding new Rx/TX callbacks > + ``virtio_recv_pkts_packed`` , ``virtio_recv_mergeable_pkts_packed`` and > + ``virtio_xmit_pkts_packed``. > + > +Virtio path number changes from release to release, all virtio paths support > +status are shown in below table:: > + > + > +--------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Virtio path\ DPDK version | v16.11 | v17.02 | v17.05 | > v17.08 | v17.11 | v18.02 | v18.05 | v18.08 | v18.11 | v19.02 | v19.05 | > v19.08 | > + > +--------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Split virtqueue mergebale path | Y | Y | Y > | Y | Y | Y | Y | Y | Y | Y | Y | Y > | s/mergebale/mergeable/ > + > +--------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Split virtqueue non-mergeable path | Y | Y | Y > | Y | Y | Y | Y | Y | Y | Y | Y | Y > | > + > +--------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Split virtqueue vectorized RX path | Y | Y | Y > | Y | Y | Y | Y | Y | Y | Y | Y | Y > | > + > ---------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Split virtqueue simple TX path | Y | Y | Y > | Y | Y | Y | Y | N | N | N | N | N > | > + > ---------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Split virtqueue in-order non-mergeable path | | | > | | | | | Y | Y | Y | Y | Y > | > + > ---------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Split virtqueue in-order mergeable path | | | > | | | | | Y | Y | Y | Y | Y > | > + > ---------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Packed virtqueue mergeable path | | | > | | | | | | | Y | Y | Y > | > + > ---------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Packed virtqueue non-mergeable path | | | > | | | | | | | Y | Y | Y > | > + > ---------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Packed virtqueue in-order mergeable path | | | > | | | | | | | Y | Y | Y > | > + > ---------------------------------------------------------------------------------------------------------------------------------------------------------+ > + |Packed virtqueue in-order non-mergeable path| | | > | | | | | | | Y | Y | Y > | > + > ---------------------------------------------------------------------------------------------------------------------------------------------------------+ > + > +QEMU Support Status > +------------------- > + > +* Qemu now support three paths of split virtqueue: Split virtqueue > mergebale path, s/support/supports/ s/mergebale/mergeable/ > + Split virtqueue no-mergeable path, Split virtqueue vectorized RX path. s/no-mergeable/non-mergeable/ > +* 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. > -- > 2.17.1 >
