Documentation/networking/napi.rst

1 .. SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
18 NAPI processing usually happens in the software interrupt context,
22 All in all NAPI abstracts away from the drivers the context and configuration
30 of the NAPI instance while the method is the driver-specific event
37 -----------
55 ------------
64 argument - drivers can process completions for any number of Tx
96    or return ``budget - 1``.
101 -------------
109 As mentioned in the :ref:`drv_ctrl` section - napi_disable() and subsequent
118 --------------------------
121 the NAPI instance - until NAPI polling finishes any further
125 to IRQ being auto-masked by the device) should use the napi_schedule_prep()
128 .. code-block:: c
130   if (napi_schedule_prep(&v->napi)) {
131       mydrv_mask_rxtx_irq(v->idx);
133       __napi_schedule(&v->napi);
138 .. code-block:: c
140   if (budget && napi_complete_done(&v->napi, work_done)) {
141     mydrv_unmask_rxtx_irq(v->idx);
142     return min(work_done, budget - 1);
146 of guarantees given by being invoked in IRQ context (no need to
151 -------------------------
153 Modern devices have multiple NAPI instances (struct napi_struct) per
156 abstraction without specific user-facing semantics. That said, most networking
175 ----------------------
178 of NAPI-related user configuration each time NAPI instances are reallocated.
202 .. code-block:: bash
204    $ kernel-source/tools/net/ynl/pyynl/cli.py \
205              --spec Documentation/netlink/specs/netdev.yaml \
206              --dump queue-get \
207              --json='{"ifindex": 2}'
213 -----------------------
226 The above parameters can also be set on a per-NAPI basis using netlink via
227 netdev-genl. When used with netlink and configured on a per-NAPI basis, the
229 ``gro-flush-timeout`` and ``napi-defer-hard-irqs``.
231 Per-NAPI configuration can be done programmatically in a user application
237 .. code-block:: bash
239   $ kernel-source/tools/net/ynl/pyynl/cli.py \
240             --spec Documentation/netlink/specs/netdev.yaml \
241             --do napi-set \
242             --json='{"id": 345,
243                      "defer-hard-irqs": 111,
244                      "gro-flush-timeout": 11111}'
246 Similarly, the parameter ``irq-suspend-timeout`` can be set using netlink
247 via netdev-genl. There is no global sysfs parameter for this value.
249 ``irq-suspend-timeout`` is used to determine how long an application can
251 which can be set on a per-epoll context basis with ``EPIOCSPARAMS`` ioctl.
256 ------------
268 epoll-based busy polling
269 ------------------------
273 all file descriptors which are added to an epoll context have the same NAPI ID.
278 the file descriptor to its epoll context. This would ensure each worker thread
279 has an epoll context with FDs that have the same NAPI ID.
289    loop waiting for events. This is a system-wide setting and will cause all
290    epoll-based applications to busy poll when they call epoll_wait. This may
293 2. Applications using recent kernels can issue an ioctl on the epoll context
297 .. code-block:: c
309 ---------------
314 Very high request-per-second applications (especially routing/forwarding
323 if ``gro_flush_timeout`` passes without any busy poll call. For epoll-based
331 with the ``SO_BUSY_POLL_BUDGET`` socket option. For epoll-based busy polling
333 in ``struct epoll_params`` and set on a specific epoll context using the ``EPIOCSPARAMS``
341 should be chosen carefully with these tradeoffs in mind. epoll-based busy
349 --------------
365   1. The per-NAPI config parameter ``irq-suspend-timeout`` should be set to the
374   2. The sysfs parameter or per-NAPI config parameters ``gro_flush_timeout``
385 userland, the ``irq-suspend-timeout`` is deferred and IRQs are disabled. This
392 It is expected that ``irq-suspend-timeout`` will be set to a value much larger
393 than ``gro_flush_timeout`` as ``irq-suspend-timeout`` should suspend IRQs for
401 irq-driven packet delivery. During busy periods, ``irq-suspend-timeout``
409 1) hardirq -> softirq -> napi poll; basic interrupt delivery
410 2) timer -> softirq -> napi poll; deferred irq processing
411 3) epoll -> busy-poll -> napi poll; busy looping
419 During busy periods, ``irq-suspend-timeout`` is used as timer in Loop 2,
426 the recommended usage, because otherwise setting ``irq-suspend-timeout``
432 -------------
435 threads rather than software IRQ context for NAPI processing.
436 The configuration is per netdevice and will affect all
438 thread (called ``napi/${ifc-name}-${napi-id}``).