mirror of
https://github.com/hardkernel/linux.git
synced 2026-06-08 03:40:35 +09:00
ce4d6fff7a
[ Upstream commit a19f89335f ]
When PREEMPT_RT is enabled, all hrtimer expiry functions are
deferred for execution into the context of ksoftirqd unless otherwise
annotated.
Deferring the expiry of the hrtimer used by the watchdog core, however,
is a waste, as the callback does nothing but queue a kthread work item
and wakeup watchdogd.
It's worst then that, too: the deferral through ksoftirqd also means
that for correct behavior a user must adjust the scheduling parameters
of both watchdogd _and_ ksoftirqd, which is unnecessary and has other
side effects (like causing unrelated expiry functions to execute at
potentially elevated priority).
Instead, mark the hrtimer used by the watchdog core as being _HARD to
allow it's execution directly from hardirq context. The work done in
this expiry function is well-bounded and minimal.
A user still must adjust the scheduling parameters of the watchdogd
to be correct w.r.t. their application needs.
Link: https://lkml.kernel.org/r/0e02d8327aeca344096c246713033887bc490dd7.1538089180.git.julia@ni.com
Cc: Guenter Roeck <linux@roeck-us.net>
Reported-and-tested-by: Steffen Trumtrar <s.trumtrar@pengutronix.de>
Reported-by: Tim Sander <tim@krieglstein.org>
Signed-off-by: Julia Cartwright <julia@ni.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
[bigeasy: use only HRTIMER_MODE_REL_HARD]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20191105144506.clyadjbvnn7b7b2m@linutronix.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Sasha Levin <sashal@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.