linux-kernel - Re: AIM7 40% regression with 2.6.26-rc1

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Message-ID: <20080507162012.GA10096@elte.hu>
Date:	Wed, 7 May 2008 18:20:12 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Matthew Wilcox <matthew@....cx>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: AIM7 40% regression with 2.6.26-rc1

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

> I think turning the BKL into a semaphore was fine per se, but that was 
> when semaphores were fast.

hm, do we know it for a fact that the 40% AIM regression is due to the 
fastpath overhead of the BKL? It would be extraordinary if so.

I think it is far more likely that it's due to the different scheduling 
and wakeup behavior of the new kernel/semaphore.c code. So the fix would 
be to restore the old scheduling behavior - that's what Yanmin's manual 
revert did and that's what got him back the previous AIM7 performance.

	Ingo
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