[dpdk-dev] [PATCH v3] doc: clarify virtio PMD path selection
Tiwei Bie
tiwei.bie at intel.com
Tue Nov 26 04:02:49 CET 2019
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.wang at intel.com>
>
> add virtio paths selection and usage introduction for better
> virtio usability.
>
> Signed-off-by: Wang Yinan <yinan.wang at 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
>
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