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Adding an unlikely() hint on the fd < 0 comparison return path improves run-time performance of the poll() system call. gcov based coverage analysis based on running stress-ng and a kernel build shows that this path return path is highly unlikely. Benchmarking on an Debian based Intel(R) Core(TM) Ultra 9 285K with a 6.15-rc1 kernel and a poll of 1024 file descriptors with zero timeout shows an call reduction from 32818 ns down to 32635 ns, which is a ~0.5% performance improvement. Results based on running 25 tests with turbo disabled (to reduce clock freq turbo changes), with 30 second run per test and comparing the number of poll() calls per second. The % standard deviation of the 25 tests was 0.08%, so results are reliable. Signed-off-by: Colin Ian King <colin.i.king@gmail.com> Link: https://lore.kernel.org/20250409155510.577490-1-colin.i.king@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.