20ab39d13e
napi_busy_loop() disables preemption and performs a NAPI poll. We can't acquire sleeping locks with disabled preemption which would be required while __napi_poll() invokes the callback of the driver. A threaded interrupt performing the NAPI-poll can be preempted on PREEMPT_RT. A RT thread on another CPU may observe NAPIF_STATE_SCHED bit set and busy-spin until it is cleared or its spin time runs out. Given it is the task with the highest priority it will never observe the NEED_RESCHED bit set. In this case the time is better spent by simply sleeping. The NET_RX_BUSY_POLL is disabled by default (the system wide sysctls for poll/read are set to zero). Disabling NET_RX_BUSY_POLL on PREEMPT_RT to avoid wrong locking context in case it is used. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Link: https://lore.kernel.org/r/20211001145841.2308454-1-bigeasy@linutronix.de Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.