From: Peter Zijlstra <peterz@infradead.org>
To: Pranith Kumar <bobby.prani@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
"maintainer:X86 ARCHITECTURE..." <x86@kernel.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
"open list:X86 ARCHITECTURE..." <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH] x86: Use volatile semantics for atomic_set()
Date: Tue, 23 Sep 2014 10:12:46 +0200 [thread overview]
Message-ID: <20140923081246.GB3312@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <CAJhHMCC7RKE9GE3fGx0pnNoZHL0r_MOPMPwCjjNNbnC6i0G=BA@mail.gmail.com>
On Mon, Sep 22, 2014 at 05:42:16PM -0400, Pranith Kumar wrote:
> On Mon, Sep 22, 2014 at 4:08 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Mon, Sep 22, 2014 at 03:39:21PM -0400, Pranith Kumar wrote:
> >> All the atomic operations have volatile semantics to prevent compiler
> >> reordering. Enforce the same semantics for atomic_set() too.
> >
> > To what point? atomic_set() is typically not what you expect it to
> > anyhow.
>
> This is the only atomic operation which allows compiler reordering. I
> am not sure why this exception was made. Any ideas as to why we do
> this?
Because it typically doesn't matter. And you should never use
atomic_set() where it does matter.
prev parent reply other threads:[~2014-09-23 8:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-22 19:39 Pranith Kumar
2014-09-22 20:08 ` Peter Zijlstra
2014-09-22 21:42 ` Pranith Kumar
2014-09-23 8:12 ` Peter Zijlstra [this message]
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