linux-kernel - Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

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Date:	Wed, 18 Apr 2007 23:48:16 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>, Nick Piggin <npiggin@...e.de>,
	William Lee Irwin III <wli@...omorphy.com>,
	Peter Williams <pwil3058@...pond.net.au>,
	Mike Galbraith <efault@....de>,
	Con Kolivas <kernel@...ivas.org>, ck list <ck@....kolivas.org>,
	Bill Huey <billh@...ppy.monkey.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [Announce] [patch] Modular Scheduler Core and Completely Fair Scheduler [CFS]

* Davide Libenzi <davidel@...ilserver.org> wrote:

> I think Ingo's idea of a new sched_group to contain the generic 
> parameters needed for the "key" calculation, works better than adding 
> more fields to existing strctures (that would, of course, host 
> pointers to it). Otherwise I can already the the struct_signal being 
> the target for other unrelated fields :)

yeah. Another detail is that for global containers like uids, the 
statistics will have to be percpu_alloc()-ed, both for correctness 
(runqueues are per CPU) and for performance.

That's one reason why i dont think it's necessarily a good idea to 
group-schedule threads, we dont really want to do a per thread group 
percpu_alloc().

In fact for threads the _reverse_ problem exists, threaded apps tend to 
_strive_ for more performance - hence their desperation of using the 
threaded programming model to begin with ;) (just think of media 
playback apps which are typically multithreaded)

I dont think threads are all that different. Also, the 
resource-conserving act of using CLONE_VM to share the VM (and to use a 
different programming environment like Java) should not be 'punished' by 
forcing the thread group to be accounted as a single, shared entity 
against other 'fat' tasks.

so my current impression is that we want per UID accounting to solve the 
X problem, the kernel threads problem and the many-users problem, but 
i'd not want to do it for threads just yet because for them there's not 
really any apparent problem to be solved.

	Ingo
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