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In vast majority of cases the condition determining whether the thread
can proceed is true after the first wake up.
However, even in that case the thread ends up calling into
prepare_to_wait_event() again, suffering a spurious irq + lock trip.
Then it calls into finish_wait() to unlink itself.
Note that in case of a pending signal the work done by
prepare_to_wait_event() gets ignored even without the change.
pre-check the condition after waking up instead.
Stats gathared during a kernel build:
bpftrace -e 'kprobe:prepare_to_wait_event,kprobe:finish_wait \
{ @[probe] = count(); }'
@[kprobe:finish_wait]: 392483
@[kprobe:prepare_to_wait_event]: 778690
As in calls to prepare_to_wait_event() almost double calls to
finish_wait(). This evens out with the patch.
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20250303230409.452687-4-mjguzik@gmail.com
Signed-off-by: Christian Brauner <brauner@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 reStructuredText 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.