linux-kernel - Re: [PATCH v3 16/22] sched: add power aware scheduling in fork/exec/wake

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Date:	Fri, 11 Jan 2013 15:08:45 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Morten Rasmussen <Morten.Rasmussen@....com>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"bp@...en8.de" <bp@...en8.de>, "pjt@...gle.com" <pjt@...gle.com>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"efault@....de" <efault@....de>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 16/22] sched: add power aware scheduling in fork/exec/wake

On 01/10/2013 11:01 PM, Morten Rasmussen wrote:
> On Sat, Jan 05, 2013 at 08:37:45AM +0000, Alex Shi wrote:
>> This patch add power aware scheduling in fork/exec/wake. It try to
>> select cpu from the busiest while still has utilization group. That's
>> will save power for other groups.
>>
>> The trade off is adding a power aware statistics collection in group
>> seeking. But since the collection just happened in power scheduling
>> eligible condition, the worst case of hackbench testing just drops
>> about 2% with powersaving/balance policy. No clear change for
>> performance policy.
>>
>> I had tried to use rq load avg utilisation in this balancing, but since
>> the utilisation need much time to accumulate itself. It's unfit for any
>> burst balancing. So I use nr_running as instant rq utilisation.
> 
> So you effective use a mix of nr_running (counting tasks) and PJT's
> tracked load for balancing?

no, just task number here.
> 
> The problem of slow reaction time of the tracked load a cpu/rq is an
> interesting one. Would it be possible to use it if you maintained a
> sched group runnable_load_avg similar to cfs_rq->runnable_load_avg where
> load contribution of a tasks is added when a task is enqueued and
> removed again if it migrates to another cpu?
> This way you would know the new load of the sched group/domain instantly
> when you migrate a task there. It might not be precise as the load
> contribution of the task to some extend depends on the load of the cpu
> where it is running. But it would probably be a fair estimate, which is
> quite likely to be better than just counting tasks (nr_running).

For power consideration scenario, it ask task number less than Lcpu
number, don't care the load weight, since whatever the load weight, the
task only can burn one LCPU.

>> +
>> +		if (sched_policy == SCHED_POLICY_POWERSAVING)
>> +			threshold = sgs.group_weight;
>> +		else
>> +			threshold = sgs.group_capacity;
> 
> Is group_capacity larger or smaller than group_weight on your platform?

Guess most of your confusing come from the capacity != weight here.

In most of Intel CPU, a cpu core's power(with 2 HT) is usually 1178, it
just bigger than a normal cpu power - 1024. but the capacity is still 1,
while the group weight is 2.

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