linux-kernel - Re: [PATCH 03 of 36] x86: add memory barriers to wrmsr

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Message-ID: <4862B3E9.50601@goop.org>
Date:	Wed, 25 Jun 2008 14:08:57 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	x86@...nel.org, xen-devel <xen-devel@...ts.xensource.com>,
	Stephen Tweedie <sct@...hat.com>,
	Eduardo Habkost <ehabkost@...hat.com>,
	Mark McLoughlin <markmc@...hat.com>
Subject: Re: [PATCH 03 of 36] x86: add memory barriers to wrmsr

Arjan van de Ven wrote:
> it's more readable for several of these cases to stick a barrier(); in
> front and after it to be honest; that makes it more explicit that
> these are deliberate compiler barriers rather than "actual" memory
> access...
>
>   

I suppose, though I would be inclined to put the barriers in the wrmsr 
macro itself to act as documentation.  Either way, I don't think there's 
any legitimate reason to let the compiler reorder things around a wrmsr, 
and it should be an inherent property of the macro, rather than relying 
on ad-hoc barriers where it gets used.  After all, that's a fairly 
accurate reflection of how the micro-architecture treats wrmsr...

    J
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