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>
---
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
+ 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.
+#. 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.
+#. 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 |
+
+--------------------------------------------------------------------------------------------------------------------------------------------------------+
+ |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,
+ Split virtqueue no-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.
--
2.17.1
