linux-kernel - Re: [PATCH RFC] Avoid memory barrier in read

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Message-ID: <CAHk-=why9gTVRPHwbyz-24QSmKW1zXrF_pbS-UtDyQddyzEu9A@mail.gmail.com>
Date: Tue, 13 Aug 2024 13:01:50 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Waiman Long <longman@...hat.com>
Cc: cl@...two.org, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Boqun Feng <boqun.feng@...il.com>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH RFC] Avoid memory barrier in read_seqcount() through load acquire

On Tue, 13 Aug 2024 at 12:58, Waiman Long <longman@...hat.com> wrote:
>
> Sorry for the confusion. What you said above is actually the reason that
> I ask this question. In the same way, smp_rmb()/wmb() is available for
> all arches. I am actually asking if it should be a flag that indicates
> the arch's preference to use acquire/release over rmb/wmb.

I think that if an arch says it has native acquire/release, we should
basically assume that it's the better model.

I mean, we could certainly use "PREFERS" instead of "HAS", but is
there any real reason to do that?

Do we suddenly expect that people would make a CPU that has native
acquire/release, and it would somehow then prefer a full read barrier?

             Linus