linux-kernel - Re: [discussion]sched: a rough proposal to enable power saving in scheduler

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Date:	Wed, 15 Aug 2012 20:24:34 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	Alex Shi <alex.shi@...el.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	vincent.guittot@...aro.org, svaidy@...ux.vnet.ibm.com,
	Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [discussion]sched: a rough proposal to enable power saving in scheduler

On 8/13/12, Alex Shi <alex.shi@...el.com> wrote:
> Since there is no power saving consideration in scheduler CFS, I has a
> very rough idea for enabling a new power saving schema in CFS.
>
> It bases on the following assumption:
> 1, If there are many task crowd in system, just let few domain cpus
> running and let other cpus idle can not save power. Let all cpu take the
> load, finish tasks early, and then get into idle. will save more power
> and have better user experience.
>
This assumption indirectly point towards the scheme when performance
is enabled, isn't it? Cause you're trying to spread the load equally
amongst all the CPUs.

> 2, schedule domain, schedule group perfect match the hardware, and
> the power consumption unit. So, pull tasks out of a domain means
> potentially this power consumption unit idle.
>
How do you plan to test this power saving scheme? Using powertop? Or,
is there any other tools?

>
> select_task_rq_fair()
> {
> 	for_each_domain(cpu, tmp) {
> 		if (policy == power && tmp_has_capacity &&
> 			 tmp->flags & sd_flag) {
> 			sd = tmp;
> 			//It is fine to got cpu in the domain
> 			break;
> 		}
> 	}
>
> 	while(sd) {
> 		if policy == power
> 			find_busiest_and_capable_group()

I'm not sure what find_busiest_and_capable_group() would really be, it
seems it'll find the busiest and capable group, but isn't it a
conflict with the first assumption you proposed on your proposal?

Thanks,
Rakib.
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