linux-kernel - Re: sched: ARM: arch_scale_freq

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Message-ID: <1318350075.14615.9.camel@twins>
Date:	Tue, 11 Oct 2011 18:21:15 +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, Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>
Subject: Re: sched: ARM: arch_scale_freq_power

On Tue, 2011-10-11 at 18:03 +0200, Vincent Guittot wrote:
> > How do you know the task is 'small' ?
> >
> 
> I want to use cpufreq to be notified that we have a large/small cpu
> load. If we have several tasks but the cpu uses the lowest frequency,
> it "should" mean that we have small tasks that are running (less than
> 20ms*95% of added duration) and we could gather them on one cpu (by
> increasing the cpu_power on a dual core).
> 
> > For that you would need to track a time-weighted effective load average
> > of the task and we don't have that.
> >
> 
> yes, that's why I use cpufreq until better option, like a
> time-weighted load average, is available 

Egads... so basically you're (ab)using the ondemand cpufreq stats to get
a guestimate of the time-weighted load of the cpu, and then (ab)use the
scheduler cpufreq hook to pump its capacity numbers.

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