Subject: Re: [RFC/RFT PATCH v3] sched: automated per tty task groups
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Mike Galbraith <efault@gmx.de>, Hans-Peter Jansen <hpj@urpla.net>,
        linux-kernel@vger.kernel.org,
        Lennart Poettering <mzxreary@0pointer.de>, david@lang.hm,
        Dhaval Giani <dhaval.giani@gmail.com>, Vivek Goyal <vgoyal@redhat.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Markus Trippelsdorf <markus@trippelsdorf.de>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Ingo Molnar <mingo@elte.hu>, Balbir Singh <balbir@linux.vnet.ibm.com>
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Date: Fri, 19 Nov 2010 12:57:24 +0100
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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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