linux-kernel - Re: sched: ARM: arch_scale_freq

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Date:	Tue, 11 Oct 2011 11:13:19 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Amit Kucheria <amit.kucheria@...aro.org>,
	linux-kernel@...r.kernel.org,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	linaro-dev@...ts.linaro.org
Subject: Re: sched: ARM: arch_scale_freq_power

On Tue, 2011-10-11 at 10:51 +0200, Vincent Guittot wrote:
> I have several goals. The 1st one is that I need to put more load on
> some cpus when I have packages with different cpu frequency.

That should be rather easy.

> I also study if I can follow the real cpu frequency but it seems to be
> not so easy.

Why not?

>  I have noticed that the cpu_power is updated periodical
> except when we have a lot of newly_idle events.

We can certainly fix that.

> Then, I have some use cases which have several running tasks but a low
> cpu load. In this case, the small tasks are spread on several cpu by
> the load_balance whereas they could be easily handled by one cpu
> without significant performance modification. 

That shouldn't be done using cpu_power, we have sched_smt_power_savings
and sched_mc_power_savings for stuff like that.

Although I would really like to kill all those different
sched_*_power_savings knobs and reduce it to one.

> If the cpu_power is
> higher than 1024, the cpu is no more seen out of capacity by the
> load_balance as soon as a short process is running and teh main result
> is that the small tasks will stay on the same cpu. This configuration
> is mainly usefull for ARM dual core system when we want to power gate
> one cpu. I use cyclictest to simulate such use case. 

Yeah, but that's wrong.

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