linux-kernel - Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock

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Date:	Tue, 13 Jul 2010 15:14:56 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Palfrader <peter@...frader.org>,
	Avi Kivity <avi@...hat.com>, Greg KH <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	stable-review@...nel.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Glauber Costa <glommer@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [patch 134/149] x86, paravirt: Add a global synchronization point
 	for pvclock

On 07/13/2010 11:21 AM, Jeremy Fitzhardinge wrote:
> 
> "asm volatile"'s only real meaning is that it will not get elided if it
> appears its output is unused (assuming it is reachable at all).  I don't
> think you can consider it having any meaningful effects on ordering.
> 

Actually, I believe volatile operations (including asm volatile) are
strictly ordered *with respect to other volatile operations*.  As such I
would think we'd want to keep the "memory" clobber here, to make it
strictly ordered with regards to *all* memory operations.

As for the concept in this patch, it's obviously the right thing, but as
Linus said elsewhere it's incomplete.

Conceptually:

Acked-by: H. Peter Anvin <hpa@...or.com>

Unfortunately I can't write the productization patch right now since I
have a plane to catch in about an hour, but if noone beats me to it I'll
to it Thursday.

	-hpa
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