linux-kernel - Re: [PATCH] checkpatch: Make the memory barrier test noisier

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Message-ID: <20130927145007.GD15690@laptop.programming.kicks-ass.net>
Date:	Fri, 27 Sep 2013 16:50:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Joe Perches <joe@...ches.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Jason Low <jason.low2@...com>,
	Davidlohr Bueso <davidlohr@...com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Alex Shi <alex.shi@...aro.org>,
	Andi Kleen <andi@...stfloor.org>,
	Michel Lespinasse <walken@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Matthew R Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Rik van Riel <riel@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH] checkpatch: Make the memory barrier test noisier

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.

> Maybe just refer to Documentation/memory-barriers.txt
> and/or say something like "please document appropriately"

Documentation/memory-barriers.txt is always good; appropriately doesn't
seem to quantify anything much at all. Someone might think:

/*  */
smp_mb();

appropriate... 

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