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

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Message-ID: <20070621202314.GA32051@elte.hu>
Date:	Thu, 21 Jun 2007 22:23:14 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Eric Dumazet <dada1@...mosbay.com>,
	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:

> On Thu, 21 Jun 2007, Ingo Molnar wrote:
> > 
> > I can understand why no data is saved by this change: gcc is 
> > aligning the next field to a natural boundary anyway and we dont 
> > really have arrays of spinlocks (fortunately).
> 
> Actually, some data structures could well shrink.
> 
> Look at "struct task_struct", for example. Right now it has two 
> spinlocks right next to each other (alloc_lock and pi_lock).

yeah. We've got init_task's task-struct embedded in the vmlinux, but 
it's aligned to 32 bytes, which probably hides this effect. We'd only 
see it if the size change just happened to bring a key data structure 
(which is also embedded in the vmlinux) just below a modulo 32 bytes 
boundary. The chance for that is around 6:32 per 'merge' event. That 
means that there cannot be all that many such cases ;-)

anyway, the shorter init sequence is worth it already.

	Ingo
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