linux-kernel - Re: [PATCH v4 1/5] asm-generic: barrier: Add smp_cond_load_relaxed

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Message-ID: <aLWDt9NpfYO_Utky@arm.com>
Date: Mon, 1 Sep 2025 12:29:59 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Ankur Arora <ankur.a.arora@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, bpf@...r.kernel.org,
	arnd@...db.de, will@...nel.org, peterz@...radead.org,
	akpm@...ux-foundation.org, mark.rutland@....com,
	harisokn@...zon.com, cl@...two.org, ast@...nel.org,
	memxor@...il.com, zhenglifeng1@...wei.com,
	xueshuai@...ux.alibaba.com, joao.m.martins@...cle.com,
	boris.ostrovsky@...cle.com, konrad.wilk@...cle.com
Subject: Re: [PATCH v4 1/5] asm-generic: barrier: Add
 smp_cond_load_relaxed_timewait()

On Fri, Aug 29, 2025 at 01:07:31AM -0700, Ankur Arora wrote:
> Add smp_cond_load_relaxed_timewait(), which extends
> smp_cond_load_relaxed() to allow waiting for a finite duration.
> 
> The additional parameter allows for the timeout check.
> 
> The waiting is done via the usual cpu_relax() spin-wait around the
> condition variable with periodic evaluation of the time-check.
> 
> The number of times we spin is defined by SMP_TIMEWAIT_SPIN_COUNT
> (chosen to be 200 by default) which, assuming each cpu_relax()
> iteration takes around 20-30 cycles (measured on a variety of x86
> platforms), amounts to around 4000-6000 cycles.
> 
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Will Deacon <will@...nel.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: linux-arch@...r.kernel.org
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>

Apart from the name, this looks fine (I'd have preferred the "timeout"
suffix).

Reviewed-by: Catalin Marinas <catalin.marinas@....com>