linux-kernel - Re: [PATCH 1/5] Add a global synchronization point for pvclock

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Message-ID: <20100419142158.GD14158@mothafucka.localdomain>
Date:	Mon, 19 Apr 2010 11:21:58 -0300
From:	Glauber Costa <glommer@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock

On Mon, Apr 19, 2010 at 02:10:54PM +0300, Avi Kivity wrote:
> On 04/19/2010 02:05 PM, Peter Zijlstra wrote:
> >>
> >>>ACCESS_ONCE() is your friend.
> >>>
> >>I think it's implied with atomic64_read().
> >Yes it would be. I was merely trying to point out that
> >
> >   last = ACCESS_ONCE(last_value);
> >
> >Is a narrower way of writing:
> >
> >   last = last_value;
> >   barrier();
> >
> >In that it need not clobber all memory locations and makes it instantly
> >clear what we want the barrier for.
> 
> Oh yes, just trying to avoid a patch with both atomic64_read() and
> ACCESS_ONCE().
you're mixing the private version of the patch you saw with this one.
there isn't any atomic reads in here. I'll use a barrier then

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