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

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Message-Id: <20080507101624.5524d3c1.akpm@linux-foundation.org>
Date:	Wed, 7 May 2008 10:16:24 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Matthew Wilcox <matthew@....cx>, Ingo Molnar <mingo@...e.hu>,
	"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 10:08:18 -0700 (PDT) Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> Which is why I'm 100% convinced it's not even worth saving the old code. 
> It needs to use mutexes, or spinlocks. I bet it has *nothing* to do with 
> "slow path" other than the fact that it gets to that slow path much more 
> these days.

Stupid question: why doesn't lock_kernel() use a mutex?

(stupid answer: it'll trigger might_sleep() checks when we do it early in
boot with irqs disabled, but we can fix that)

(And __might_sleep()'s system_state check might even save us from that)

Of course, we shouldn't change anything until we've worked out why the new
semaphores got slower.

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