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The global hash_lock protecting the posix timer hash table can be heavily contended especially when there is an extensive linear search for a timer ID. Timer IDs are handed out by monotonically increasing next_posix_timer_id and then validating that there is no timer with the same ID in the hash table. Both operations happen with the global hash lock held. To reduce the hash lock contention the hash will be reworked to a scaled hash with per bucket locks, which requires to handle the ID counter lockless. Prepare for this by making next_posix_timer_id an atomic_t, which can be used lockless with atomic_inc_return(). [ tglx: Adopted from Eric's series, massaged change log and simplified it ] Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Acked-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lore.kernel.org/all/20250219125522.2535263-2-edumazet@google.com Link: https://lore.kernel.org/all/20250308155624.151545978@linutronix.de
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.