linux-kernel - Re: [PATCH] x86: Make variable_test

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Message-ID: <9d5b1868-51f5-4d88-8b0e-813e32b05a96@email.android.com>
Date:	Thu, 06 Oct 2011 20:13:38 -0700
From:	"hpanvin@...il.com" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Josh Stone <jistone@...hat.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Jakub Jelinek <jakub@...hat.com>
Subject: Re: [PATCH] x86: Make variable_test_bit reference all of *addr

Memory clobbers are universal producers, not consumers.

Andi Kleen <andi@...stfloor.org> wrote:

>"hpanvin@...il.com" <hpa@...or.com> writes:
>
>
>> This is concerning... the kernel relies heavily on asm volatile being
>a universal memory consumer.  If that is suddenly broken, we are f***
>in many, many, MANY places in the kernel all of a sudden!
>
>I don't think that's true. We generally add "memory" clobbers for this
>purpose. asm volatile just means "don't move" 
>
>Just this one doesn't have it for unknown reasons (someone
>overoptimizing?)
>
>-Andi
>
>-- 
>ak@...ux.intel.com -- Speaking for myself only

-- 
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