linux-kernel - Re: [PATCH] do_wait wakeup optimization

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Date:	Wed, 19 Nov 2008 19:35:45 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Roland McGrath <roland@...hat.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ratan Nalumasu <rnalumasu@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] do_wait wakeup optimization



On Wed, 19 Nov 2008, Roland McGrath wrote:
>
> Ratan Nalumasu reported that in a process with many threads doing
> different, mutually-exclusive waitpid() calls, there were a lot of
> unnecessary wakeups.  Every waiting thread in the process wakes up to
> loop through the children and see that the only ones it cares about
> are still not ready.

Patch looks sane, and look worth queueing up for the next merge window. 
But if somebody actually has numbers and/or can talk about the real-life 
load that made people even notice this, that would be good to add to the 
description.

Also, do we really need to call eligible_child() twice? The real wait only 
does it once in that "wait_consider_task()". Explanations would be good..

			Linus
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