linux-kernel - Re: [patch V3 11/18] posix-timers: Make signal_struct:: Next_posix_timer_id an atomic

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Message-ID: <Z9A9ci9kh55q-ax_@localhost.localdomain>
Date: Tue, 11 Mar 2025 14:41:06 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Benjamin Segall <bsegall@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Andrey Vagin <avagin@...nvz.org>,
	Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Cyrill Gorcunov <gorcunov@...il.com>
Subject: Re: [patch V3 11/18] posix-timers: Make signal_struct::
 Next_posix_timer_id an atomic_t

Le Sat, Mar 08, 2025 at 05:48:36PM +0100, Thomas Gleixner a écrit :
> From: Eric Dumazet <edumazet@...gle.com>
> 
> 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@...gle.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Link: https://lore.kernel.org/all/20250219125522.2535263-2-edumazet@google.com

Acked-by: Frederic Weisbecker <frederic@...nel.org>