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Miller" , Eric Dumazet , Simon Horman , Jonathan Corbet , linux-doc@vger.kernel.org (open list:DOCUMENTATION), linux-kernel@vger.kernel.org (open list) Subject: [PATCH net-next v3] documentation: networking: Add NAPI config Date: Thu, 13 Feb 2025 19:15:34 +0000 Message-ID: <20250213191535.38792-1-jdamato@fastly.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: kuba@kernel.org 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 Acked-by: Jakub Kicinski Reviewed-by: Bagas Sanjaya --- v3: - Add tags from Jakub and Bagas. v2: - Reword the Persistent Napi config section using some suggestions from Jakub. Documentation/networking/napi.rst | 33 ++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) base-commit: 4079918ae720e842ed7dff65fedeb9980b374995 diff --git a/Documentation/networking/napi.rst b/Documentation/networking/napi.rst index f970a2be271a..d0e3953cae6a 100644 --- a/Documentation/networking/napi.rst +++ b/Documentation/networking/napi.rst @@ -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 -----------------------