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Subject: Re: [PATCH] checkpatch: Make the memory barrier test noisier
From: Oliver Neukum <oliver@neukum.org>
Date: Sat, 28 Sep 2013 01:40:27 +0200
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Joe Perches <joe@perches.com>, Ingo Molnar <mingo@kernel.org>, Tim Chen <tim.c.chen@linux.intel.com>, Jason Low <jason.low2@hp.com>, Davidlohr Bueso <davidlohr@hp.com>, Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>, Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@linaro.org>, Andi Kleen <andi@firstfloor.org>, Michel Lespinasse <walken@google.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Rik van Riel <riel@redhat.com>, Peter Hurley <peter@hurleysoftware.com>, linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>

On Fri, 2013-09-27 at 16:50 +0200, Peter Zijlstra wrote:
> On Fri, Sep 27, 2013 at 07:34:55AM -0700, Joe Perches wrote:
> > That would make it seem as if all barriers are SMP no?
> 
> I would think any memory barrier is ordering against someone else; if
> not smp then a device/hardware -- like for instance the hardware page
> table walker.
> 
> Barriers are fundamentally about order; and order only makes sense if
> there's more than 1 party to the game.

But not necessarily more than 1 kind of parties. It is perfectly
possible to have a barrier against other threads running the same
function.

	Regards
		Oliver


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