linux-kernel - Re: [git pull] scheduler fixes

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Date:	Tue, 13 May 2008 16:11:29 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Sven Wegener <sven.wegener@...aler.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Andi Kleen <andi@...stfloor.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Viro <viro@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [git pull] scheduler fixes


* Matthew Wilcox <matthew@....cx> wrote:

> > So why not transform it to real completions instead? And if our 
> > current 'struct completion' abstraction is insufficient for whatever 
> > reason, why not extend that instead?
> 
> My point is that for the only user of counting semaphores and/or 
> semaphores-abused-as-completions that has so far hit this race, the 
> serialised wake-up performs better.  You have not pointed at a 
> scenario that _shows_ a parallel wake-up to perform better. [...]

a 50% AIM7 slowdown maybe? With the BKL being a spinlock again it doesnt 
matter much in practice though.

	Ingo
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