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documentation: networking: Add NAPI config

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Document the existence of persistent per-NAPI configuration space and
the API that drivers can opt into.

Update stale documentation which suggested that NAPI IDs cannot be
queried from userspace.

Signed-off-by: Joe Damato <jdamato@fastly.com>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://patch.msgid.link/20250213191535.38792-1-jdamato@fastly.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Joe Damato
2025-02-13 19:15:34 +00:00
committed by Jakub Kicinski
parent 6041d8bf32
commit bf1b8e0abc
1 changed files with 32 additions and 1 deletions
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33
Documentation/networking/napi.rst
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@@ -171,12 +171,43 @@ a channel as an IRQ/NAPI which services queues of a given type. For example,
a configuration of 1 ``rx``, 1 ``tx`` and 1 ``combined`` channel is expected
to utilize 3 interrupts, 2 Rx and 2 Tx queues.
Persistent NAPI config
----------------------
Drivers often allocate and free NAPI instances dynamically. This leads to loss
of NAPI-related user configuration each time NAPI instances are reallocated.
The netif_napi_add_config() API prevents this loss of configuration by
associating each NAPI instance with a persistent NAPI configuration based on
a driver defined index value, like a queue number.
Using this API allows for persistent NAPI IDs (among other settings), which can
be beneficial to userspace programs using ``SO_INCOMING_NAPI_ID``. See the
sections below for other NAPI configuration settings.
Drivers should try to use netif_napi_add_config() whenever possible.
User API
========
User interactions with NAPI depend on NAPI instance ID. The instance IDs
are only visible to the user thru the ``SO_INCOMING_NAPI_ID`` socket option.
It's not currently possible to query IDs used by a given device.
Users can query NAPI IDs for a device or device queue using netlink. This can
be done programmatically in a user application or by using a script included in
the kernel source tree: ``tools/net/ynl/pyynl/cli.py``.
For example, using the script to dump all of the queues for a device (which
will reveal each queue's NAPI ID):
.. code-block:: bash
$ kernel-source/tools/net/ynl/pyynl/cli.py \
--spec Documentation/netlink/specs/netdev.yaml \
--dump queue-get \
--json='{"ifindex": 2}'
See ``Documentation/netlink/specs/netdev.yaml`` for more details on
available operations and attributes.
Software IRQ coalescing
-----------------------