linux-kernel - Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

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Message-ID: <1290167844.2109.1560.camel@laptop>
Date:	Fri, 19 Nov 2010 12:57:24 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Samuel Thibault <samuel.thibault@...-lyon.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mike Galbraith <efault@....de>,
	Hans-Peter Jansen <hpj@...la.net>,
	linux-kernel@...r.kernel.org,
	Lennart Poettering <mzxreary@...inter.de>, david@...g.hm,
	Dhaval Giani <dhaval.giani@...il.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Ingo Molnar <mingo@...e.hu>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>
Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups

On Fri, 2010-11-19 at 01:07 +0100, Samuel Thibault wrote:
> 
> 
> Also note that having a hierarchical process structure should permit to
> make things globally more efficient: avoid putting e.g. your cpp, cc1,
> and asm processes at three corners of your 4-socket NUMA machine :) 

We have the hierarchy mandated by POSIX to track parents, childs,
sessions and all that stuff, its just not the data structure used for
scheduling.

And no, using that to load-balance between CPUs doesn't necessarily help
with the NUMA case, load-balancing is an impossible job (equivalent to
page-replacement -- you simply don't know the future), applications
simply do wildly weird stuff. 

>From a process hierarchy there's absolutely no difference between a
cc1/cpp/asm and some MPI jobs, both can be parent-child relations with
pipes between, some just run short and have data affinity, others run
long and don't have any.


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