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

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Message-ID: <87ecsor126.fsf@oracle.com>
Date: Tue, 02 Sep 2025 14:34:25 -0700
From: Ankur Arora <ankur.a.arora@...cle.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Ankur Arora <ankur.a.arora@...cle.com>, 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()


Catalin Marinas <catalin.marinas@....com> writes:

> 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).

So, the suffix "timewait" made sense to me because I was trying to
differentiate with spinwait etc.

Given that that issue is no longer meaningful, "timeout" makes more sense.

Will change.

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

Thanks for this and all the reviews.

--
ankur