linux-kernel - Re: [REPORT] cfs-v4 vs sd-0.44

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Message-ID: <alpine.LFD.0.98.0704210931370.9964@woody.linux-foundation.org>
Date:	Sat, 21 Apr 2007 09:34:07 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Willy Tarreau <w@....eu>
cc:	Ingo Molnar <mingo@...e.hu>, Con Kolivas <kernel@...ivas.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Gene Heskett <gene.heskett@...il.com>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44



On Sat, 21 Apr 2007, Willy Tarreau wrote:
> 
> If you remember, with 50/50, I noticed some difficulties to fork many
> processes. I think that during a fork(), the parent has a higher probability
> of forking other processes than the child. So at least, we should use
> something like 67/33 or 75/25 for parent/child.

It would be even better to simply have the rule:
 - child gets almost no points at startup
 - but when a parent does a "waitpid()" call and blocks, it will spread 
   out its points to the childred (the "vfork()" blocking is another case 
   that is really the same).

This is a very special kind of "priority inversion" logic: you give higher 
priority to the things you wait for. Not because of holding any locks, but 
simply because a blockign waitpid really is a damn big hint that "ok, the 
child now works for the parent".

		Linus
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