From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Douglas Hatch <doug.hatch@hp.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>, Waiman Long <Waiman.Long@hp.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Norton, Scott J" <scott.norton@hp.com>,
Peter Anvin <hpa@zytor.com>,
"linux-tip-commits@vger.kernel.org"
<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:locking/core] locking/pvqspinlock: Replace xchg() by the more descriptive set_mb()
Date: Tue, 12 May 2015 15:00:43 +0200 [thread overview]
Message-ID: <20150512130043.GF16478@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150512084529.GC21418@twins.programming.kicks-ass.net>
On Tue, May 12, 2015 at 10:45:29AM +0200, Peter Zijlstra wrote:
> On Mon, May 11, 2015 at 10:50:42AM -0700, Linus Torvalds wrote:
> > On Mon, May 11, 2015 at 7:54 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > >
> > > Hmm, so I looked at the set_mb() definitions and I figure we want to do
> > > something like the below, right?
> >
> > I don't think you need to do this for the non-smp cases.
>
> Well, its the store tearing thing again, we use WRITE_ONCE() in
> smp_store_release() for the same reason. We want it to be a single
> store.
>
> > The whole
> > thing is about smp memory ordering, so on UP you don't even need the
> > WRITE_ONCE(), much less a barrier.
Ah, you meant the memory barrier; indeed, a compiler barrier is
sufficient. I got somewhat confused between Waiman's email and barrier
and barrier() (again!).
next prev parent reply other threads:[~2015-05-12 13:01 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <tip-52c9d2badd1ae4d11c29de57d4e964e48afd3cb4@git.kernel.org>
2015-05-11 14:54 ` [tip:locking/core] locking/pvqspinlock: Replace xchg() by the more descriptive set_mb() Peter Zijlstra
2015-05-11 16:50 ` Waiman Long
2015-05-11 17:50 ` Linus Torvalds
2015-05-12 8:45 ` Peter Zijlstra
2015-05-12 13:00 ` Peter Zijlstra [this message]
2015-05-12 8:53 ` Peter Zijlstra
2015-05-12 14:59 ` Peter Zijlstra
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