linux-kernel - Re: [PATCH 0/3] sched: use EDF to throttle RT task groups v2

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Date:	Tue, 23 Mar 2010 21:56:23 +0100
From:	Dhaval Giani <dhaval@...is.sssup.it>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Fabio Checconi <fchecconi@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>,
	Dario Faggioli <faggioli@...dalf.sssup.it>,
	Michael Trimarchi <michael@...dence.eu.com>,
	Tommaso Cucinotta <t.cucinotta@...up.it>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] sched: use EDF to throttle RT task groups v2

> > The biggest problem with the four files used in the current implementation
> > is that bandwidth assignments should be atomic (because setting all the
> > parameters independently can force the system to go through non-feasible
> > assignments, and the order to use when assigning runtime and period
> > changes depending on the direction of the change).  I know this is a
> > dangerous question, but I'll try it anyway: are we ready for multi-valued
> > cgroup parameters?
> 
> Right, I don't know about multi-valued files, that sounds like its going
> to confuse people too.
> 

True, but after having used the current interface I feel multi-valued
files will be better. For an idea, this is how I currently change
bandwidth allocated to a group.

(I am ignoring cpu.rt_ prefixes and _us suffixes for the filenames)

Starting state: task_runtime: 100000, task_period: 1000000.
runtime=200000, period=1000000

Suppose I want to bring down the periods to 100000, then first I need
to change task_runtime to 10000, then the task period, then the runtime
and finally the period.

If I want to go the opposite way, then first I need to increase the
periods and then the runtimes.

But I can also see why one would not want a multi-valued interface, esp
when the idea is just to change the runtimes. (though there is a
complicated interaction between task_runtime and runtime which I am not
sure how to avoid).

IOW, this interface sucks :-). We really need something better and
easier to use. (Sorry for no constructive input)

Thanks,
Dhaval
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