From: Peter Zijlstra <peterz@infradead.org>
To: "Christoph Lameter (Ampere)" <cl@gentwo.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Will Deacon <will@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Catalin Marinas <catalin.marinas@arm.com>,
Ingo Molnar <mingo@redhat.com>, Waiman Long <longman@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH v3] Avoid memory barrier in read_seqcount() through load acquire
Date: Fri, 25 Oct 2024 09:42:44 +0200 [thread overview]
Message-ID: <20241025074244.GB14555@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <e9fd5ba0-bd84-76a8-a96e-1378c66d0774@gentwo.org>
On Wed, Oct 23, 2024 at 04:42:36PM -0700, Christoph Lameter (Ampere) wrote:
> On Wed, 23 Oct 2024, Peter Zijlstra wrote:
>
> > > I doubt anybody will notice, and smp_load_acquire() is the future. Any
> > > architecture that does badly on it just doesn't matter (and, as
> > > mentioned, I don't think they even exist - "smp_rmb()" is generally at
> > > least as expensive).
> >
> > Do we want to do the complementing patch and make write_seqcount_end()
> > use smp_store_release() ?
> >
> > I think at least ARM (the 32bit thing) has wmb but uses mb for
> > store_release. But I also think I don't really care about that.
>
> The proper instruction would be something like
>
> atomic_inc_release(&seqcount)
It would not be, making the increment itself atomic would make the whole
thing far more expensive.
next prev parent reply other threads:[~2024-10-25 7:42 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-12 22:44 Christoph Lameter via B4 Relay
2024-09-13 13:41 ` kernel test robot
2024-09-16 17:52 ` Christoph Lameter (Ampere)
2024-09-17 7:37 ` Will Deacon
2024-09-17 11:50 ` Thomas Gleixner
2024-09-18 0:45 ` Vivi, Rodrigo
2024-09-13 13:41 ` kernel test robot
2024-09-17 7:12 ` Will Deacon
2024-09-18 11:03 ` Christoph Lameter (Ampere)
2024-09-18 15:22 ` Linus Torvalds
2024-09-23 16:28 ` Linus Torvalds
2024-10-23 19:45 ` Peter Zijlstra
2024-10-23 20:34 ` Linus Torvalds
2024-10-28 14:10 ` Will Deacon
2024-10-23 23:42 ` Christoph Lameter (Ampere)
2024-10-25 7:42 ` Peter Zijlstra [this message]
2024-10-25 19:30 ` Christoph Lameter (Ampere)
2024-09-17 11:52 ` Thomas Gleixner
2024-09-18 11:11 ` Christoph Lameter (Ampere)
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