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Date: Wed, 7 May 2008 18:20:12 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>, Matthew Wilcox <matthew@wil.cx>,
       "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
       LKML <linux-kernel@vger.kernel.org>,
       Alexander Viro <viro@ftp.linux.org.uk>,
       Andrew Morton <akpm@linux-foundation.org>
Subject: Re: AIM7 40% regression with 2.6.26-rc1
Message-ID: <20080507162012.GA10096@elte.hu>
References: <1210052904.3453.30.camel@ymzhang> <20080506114449.GC32591@elte.hu> <1210126286.3453.37.camel@ymzhang> <1210131712.3453.43.camel@ymzhang> <87lk2mbcqp.fsf@basil.nowhere.org> <20080507114643.GR19219@parisc-linux.org> <87hcdab8zp.fsf@basil.nowhere.org> <alpine.LFD.1.10.0805070728280.32269@woody.linux-foundation.org>
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* Linus Torvalds <torvalds@linux-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