Re: [PATCH] sched: Remove ACCESS_ONCE() for jiffies

From: Pranith Kumar
Date: Tue Aug 12 2014 - 10:43:34 EST

On Tue, Aug 12, 2014 at 1:55 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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().

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