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

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Message-ID: <alpine.LFD.1.10.0805071125090.3024@woody.linux-foundation.org>
Date:	Wed, 7 May 2008 11:27:21 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Matthew Wilcox <matthew@....cx>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"J. Bruce Fields" <bfields@...i.umich.edu>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@....linux.org.uk>,
	linux-fsdevel@...r.kernel.org
Subject: Re: AIM7 40% regression with 2.6.26-rc1



On Wed, 7 May 2008, Ingo Molnar wrote:
> 
> [ this patch should in fact be a bit worse, because there's two more 
>   atomics in the fastpath - the fastpath atomics of the old semaphore 
>   code. ]

Well, it doesn't have the irq stuff, which is also pretty costly. Also, it 
doesn't nest the accesses the same way (with the counts being *inside* the 
spinlock and serialized against each other), so I'm not 100% sure you'd 
get the same behaviour.

But yes, it certainly has the potential to show the same slowdown. But 
it's not a very good patch, since not showing it doesn't really prove 
much.

			Linus
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