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Diffstat (limited to 'Documentation/networking/napi.rst')
| -rw-r--r-- | Documentation/networking/napi.rst | 44 |
1 files changed, 41 insertions, 3 deletions
diff --git a/Documentation/networking/napi.rst b/Documentation/networking/napi.rst index 6083210ab2a4..a15754adb041 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 ----------------------- @@ -362,7 +393,7 @@ It is expected that ``irq-suspend-timeout`` will be set to a value much larger than ``gro_flush_timeout`` as ``irq-suspend-timeout`` should suspend IRQs for the duration of one userland processing cycle. -While it is not stricly necessary to use ``napi_defer_hard_irqs`` and +While it is not strictly necessary to use ``napi_defer_hard_irqs`` and ``gro_flush_timeout`` to use IRQ suspension, their use is strongly recommended. @@ -413,7 +444,14 @@ dependent). The NAPI instance IDs will be assigned in the opposite order than the process IDs of the kernel threads. Threaded NAPI is controlled by writing 0/1 to the ``threaded`` file in -netdev's sysfs directory. +netdev's sysfs directory. It can also be enabled for a specific NAPI using +netlink interface. + +For example, using the script: + +.. code-block:: bash + + $ ynl --family netdev --do napi-set --json='{"id": 66, "threaded": 1}' .. rubric:: Footnotes |