linux-kernel - Re: [patch v5 14/15] sched: power aware load balance

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Date:	Sat, 30 Mar 2013 21:01:56 +0530
From:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
To:	Alex Shi <alex.shi@...el.com>
CC:	mingo@...hat.com, peterz@...radead.org, efault@....de,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com, bp@...en8.de,
	pjt@...gle.com, namhyung@...nel.org, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, viresh.kumar@...aro.org,
	linux-kernel@...r.kernel.org, morten.rasmussen@....com
Subject: Re: [patch v5 14/15] sched: power aware load balance

Hi,

On 03/30/2013 07:34 PM, Alex Shi wrote:
> On 03/30/2013 07:25 PM, Preeti U Murthy wrote:
>>>> I still give the rq->util weight even the nr_running is 0, because some
>>>> transitory tasks may actived on the cpu, but just missed on balancing point.
>>>>
>>>> I just wondering that forgetting rq->util when nr_running = 0 is the
>>>> real root cause if your finding is just on VM and without fixed VCPU to
>>>> CPU pin.
>> I find the same situation on a physical machine too. On a 2 socket, 4
>> core machine as well. In fact, using trace_printks in the load balancing
>> part, I could find that the reason that the load was not getting
>> consolidated onto a socket was because the rq->util of a run-queue with
>> no processes on it, had not decayed to 0, which is why it would consider
>> the socket as overloaded and would  rule out power aware balancing.All
>> this was on a physical machine.
> 
> Consider of this situation, we may stop account the rq->util when
> nr_running is zero. Tasks will be a bit more compact. but anyway, that's
> powersaving policy.
> 
True, the tasks will be packed a bit more compactly, but we can expect
the behaviour of your patchset *defaulting to performance policy when
overloaded*, to come to the rescue of such a situation.

Regards
Preeti U Murthy

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