linux-kernel - Re: [BUG] long freezes on thinkpad t60

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Date:	Thu, 21 Jun 2007 22:18:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Chuck Ebbert <cebbert@...hat.com>, Jarek Poplawski <jarkao2@...pl>,
	Miklos Szeredi <miklos@...redi.hu>, chris@...ee.ca,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	akpm@...ux-foundation.org
Subject: Re: [BUG] long freezes on thinkpad t60


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> No, the cache line arbitration doesn't know anything about "locked" vs 
> "unlocked" instructions (it could, but there really is no point).
> 
> The real issue is that locked instructions on x86 are serializing, 
> which makes them extremely slow (compared to just a write), and then 
> by being slow they effectively just make the window for another core 
> bigger.
> 
> IOW, it doesn't "fix" anything, it just hides the bug with timing.

yeah. I think Linux is i think the only OS on the planet that is using 
the movb trick for unlock, it even triggered a hardware erratum ;) So it 
might surprise some hw makers who might rely on the heuristics that each 
critical section lock and unlock is a LOCK-ed instruction.

	Ingo
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