linux-kernel - Re: [PATCH] sched: Remove ACCESS

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Message-ID: <CAJhHMCAk3VQVE_wqojF48ozB52igHGGdJQQVV+rrOCFTf-RqdQ@mail.gmail.com>
Date:	Tue, 12 Aug 2014 10:42:45 -0400
From:	Pranith Kumar <bobby.prani@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	"open list:SCHEDULER" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Remove ACCESS_ONCE() for jiffies

On Tue, Aug 12, 2014 at 1:55 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Aug 11, 2014 at 06:51:41PM -0400, Pranith Kumar wrote:
>> jiffies is declared as a volatile variable. Therefore it is not neccessary to
>> use ACCESS_ONCE() while reading it.
>
> It also doesn't hurt and it documents intent, so I'm inclined to keep
> it.

It looks more like an inconsistency. These are the only three places
which use ACCESS_ONCE() for jiffies. Also, in doc/memory-barriers.txt,
it explicitly states that ACCESS_ONCE(jiffies) is not necessary. I
grepped for this usage after reading that document just to make sure
and found these three uses.

But yes, there is no harm being done by using ACCESS_ONCE().

-- 
Pranith
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