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Date: Sat, 21 Apr 2007 09:42:41 -0700
From: William Lee Irwin III <wli@holomorphy.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Willy Tarreau <w@1wt.eu>, Ingo Molnar <mingo@elte.hu>,
       Con Kolivas <kernel@kolivas.org>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@linux-foundation.org>,
       Nick Piggin <npiggin@suse.de>, Mike Galbraith <efault@gmx.de>,
       Arjan van de Ven <arjan@infradead.org>,
       Peter Williams <pwil3058@bigpond.net.au>,
       Thomas Gleixner <tglx@linutronix.de>, caglar@pardus.org.tr,
       Gene Heskett <gene.heskett@gmail.com>
Subject: Re: [REPORT] cfs-v4 vs sd-0.44
Message-ID: <20070421164241.GF2986@holomorphy.com>
References: <20070420140457.GA14017@elte.hu> <20070421121235.GA2044@1wt.eu> <20070421154614.GA26169@elte.hu> <20070421161818.GC7840@1wt.eu> <alpine.LFD.0.98.0704210931370.9964@woody.linux-foundation.org>
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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.

On Sat, Apr 21, 2007 at 09:34:07AM -0700, Linus Torvalds wrote:
> 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".

An in-kernel scheduler API might help. void yield_to(struct task_struct *)?

A userspace API might be nice, too. e.g. int sched_yield_to(pid_t).


-- wli