From: Waiman Long <longman@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: cl@gentwo.org, Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Boqun Feng <boqun.feng@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RFC] Avoid memory barrier in read_seqcount() through load acquire
Date: Tue, 13 Aug 2024 16:23:54 -0400 [thread overview]
Message-ID: <b770230f-7721-461b-a9f8-b482284c4a94@redhat.com> (raw)
In-Reply-To: <CAHk-=why9gTVRPHwbyz-24QSmKW1zXrF_pbS-UtDyQddyzEu9A@mail.gmail.com>
On 8/13/24 16:01, Linus Torvalds wrote:
> On Tue, 13 Aug 2024 at 12:58, Waiman Long <longman@redhat.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?
ARCH_HAS_ACQUIRE_RELEASE is fine, but the help text for this Kconfig option should clarify this preference as both the ARCH_HAS_ACQUIRE_RELEASE and the !ARCH_HAS_ACQUIRE_RELEASE code are valid.
Cheers,
Longman
next prev parent reply other threads:[~2024-08-13 20:24 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-08-13 18:26 Christoph Lameter via B4 Relay
2024-08-13 19:01 ` Waiman Long
2024-08-13 19:41 ` Christoph Lameter (Ampere)
2024-08-13 19:48 ` Linus Torvalds
2024-08-13 19:58 ` Waiman Long
2024-08-13 20:01 ` Linus Torvalds
2024-08-13 20:23 ` Waiman Long [this message]
2024-08-19 8:45 ` Mark Rutland
2024-08-19 16:25 ` Linus Torvalds
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