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

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Message-ID: <CAHk-=whgwpzsn9XvZt3zRgP87r4mSScD04P_g5JeiR1irN3vRA@mail.gmail.com>
Date: Tue, 13 Aug 2024 12:48:09 -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 12:01, Waiman Long <longman@...hat.com> wrote:
>
> Do we need a new ARCH flag?

I'm confused by that question.

That's clearly exactly what that ARCH_HAS_ACQUIRE_RELEASE is.

Obviously all architectures "have" it - in the sense that we always
have access to a "smp_load_acquire()/smp_store_release()".

But if the architecture doesn't support it natively, the old rmb/wmb
model may be preferred.

Although maybe we're at the point where we don't even care about that.

              Linus