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

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Date:	Sat, 21 Apr 2007 18:53:26 +0200
From:	Willy Tarreau <w@....eu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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, Apr 21, 2007 at 09:34:07AM -0700, Linus Torvalds wrote:
> 
> 
> 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".

I like this idea a lot. I don't know if it can be applied to pipes and unix
sockets, but it's clearly a way of saying "hurry up, I'm waiting for you"
which seems natural with inter-process communications. Also, if we can do
this on unix sockets, it would help a lot with X !

Willy

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