From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Anna-Maria Behnsen <anna-maria@linutronix.de>,
Benjamin Segall <bsegall@google.com>,
Eric Dumazet <edumazet@google.com>,
Andrey Vagin <avagin@openvz.org>,
Pavel Tikhomirov <ptikhomirov@virtuozzo.com>,
Peter Zijlstra <peterz@infradead.org>,
Cyrill Gorcunov <gorcunov@gmail.com>
Subject: Re: [patch V3 14/18] posix-timers: Avoid false cacheline sharing
Date: Tue, 11 Mar 2025 14:53:18 +0100 [thread overview]
Message-ID: <Z9BATkiH4LLpt1C6@localhost.localdomain> (raw)
In-Reply-To: <20250308155624.341108067@linutronix.de>
Le Sat, Mar 08, 2025 at 05:48:42PM +0100, Thomas Gleixner a écrit :
> struct k_itimer has the hlist_node, which is used for lookup in the hash
> bucket, and the timer lock in the same cache line.
>
> That's obviously bad, if one CPU fiddles with a timer and the other is
> walking the hash bucket on which that timer is queued.
>
> Avoid this by restructuring struct k_itimer, so that the read mostly (only
> modified during setup and teardown) fields are in the first cache line and
> the lock and the rest of the fields which get written to are in cacheline
> 2-N.
>
> Reduces cacheline contention in a test case of 64 processes creating and
> accessing 20000 timers each by almost 30% according to perf.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Impressive what a fields reshuffle and alignement can achieve!
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
next prev parent reply other threads:[~2025-03-11 13:53 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-03-08 16:48 [patch V3 00/18] posix-timers: Rework the global hash table and provide a sane mechanism for CRIU Thomas Gleixner
2025-03-08 16:48 ` [patch V3 01/18] posix-timers: Ensure that timer initialization is fully visible Thomas Gleixner
2025-03-08 21:39 ` Frederic Weisbecker
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 02/18] posix-timers: Initialise timer before adding it to the hash table Thomas Gleixner
2025-03-11 13:25 ` Frederic Weisbecker
2025-03-11 14:16 ` Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Eric Dumazet
2025-03-08 16:48 ` [patch V3 03/18] posix-timers: Add cond_resched() to posix_timer_add() search loop Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Eric Dumazet
2025-03-08 16:48 ` [patch V3 04/18] posix-timers: Cleanup includes Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 05/18] posix-timers: Remove a few paranoid warnings Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 06/18] posix-timers: Remove SLAB_PANIC from kmem cache Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 07/18] posix-timers: Use guards in a few places Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 08/18] posix-timers: Simplify lock/unlock_timer() Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 09/18] posix-timers: Rework timer removal Thomas Gleixner
2025-03-09 23:17 ` Frederic Weisbecker
2025-03-10 6:33 ` Thomas Gleixner
2025-03-10 8:13 ` [patch V3a " Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 10/18] posix-timers: Make lock_timer() use guard() Thomas Gleixner
2025-03-10 11:57 ` Frederic Weisbecker
2025-03-10 17:36 ` Thomas Gleixner
2025-03-10 22:16 ` Frederic Weisbecker
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Peter Zijlstra
2025-03-08 16:48 ` [patch V3 11/18] posix-timers: Make signal_struct:: Next_posix_timer_id an atomic_t Thomas Gleixner
2025-03-10 22:57 ` Frederic Weisbecker
2025-03-11 13:41 ` Frederic Weisbecker
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Eric Dumazet
2025-03-08 16:48 ` [patch V3 12/18] posix-timers: Improve hash table performance Thomas Gleixner
2025-03-11 13:44 ` Frederic Weisbecker
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 13/18] posix-timers: Switch to jhash32() Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 14/18] posix-timers: Avoid false cacheline sharing Thomas Gleixner
2025-03-11 13:53 ` Frederic Weisbecker [this message]
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-13 22:13 ` [patch V3 14/18] " David Laight
2025-03-17 6:20 ` Nysal Jan K.A.
2025-03-08 16:48 ` [patch V3 15/18] posix-timers: Make per process list RCU safe Thomas Gleixner
2025-03-11 15:29 ` Frederic Weisbecker
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 16/18] posix-timers: Dont iterate /proc/$PID/timers with sighand:: Siglock held Thomas Gleixner
2025-03-08 22:38 ` Cyrill Gorcunov
2025-03-11 15:26 ` Frederic Weisbecker
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-08 16:48 ` [patch V3 17/18] posix-timers: Provide a mechanism to allocate a given timer ID Thomas Gleixner
2025-03-08 22:25 ` Cyrill Gorcunov
2025-03-11 21:35 ` Frederic Weisbecker
2025-03-11 22:05 ` Thomas Gleixner
2025-03-11 22:07 ` [patch V3a " Thomas Gleixner
2025-03-11 22:32 ` Frederic Weisbecker
2025-03-12 7:56 ` Cyrill Gorcunov
2025-03-12 11:24 ` Thomas Gleixner
2025-03-12 11:31 ` Thomas Gleixner
2025-03-12 12:41 ` Cyrill Gorcunov
2025-03-12 17:45 ` Thomas Gleixner
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
2025-03-12 12:59 ` [patch V3 17/18] " Cyrill Gorcunov
2025-03-08 16:48 ` [patch V3 18/18] selftests/timers/posix-timers: Add a test for exact allocation mode Thomas Gleixner
2025-03-10 8:11 ` [patch V3a " Thomas Gleixner
2025-03-11 21:44 ` Frederic Weisbecker
2025-03-13 11:31 ` [tip: timers/core] " tip-bot2 for Thomas Gleixner
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