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

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Message-ID: <514AE07A.10100@linux.vnet.ibm.com>
Date:	Thu, 21 Mar 2013 15:57:06 +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

On 03/21/2013 02:57 PM, Alex Shi wrote:
> On 03/21/2013 04:41 PM, Preeti U Murthy wrote:
>>>>
>> Yes, I did find this behaviour on a 2 socket, 8 core machine very
>> consistently.
>>
>> rq->util cannot go to 0, after it has begun accumulating load right?
>>
>> Say a load was running on a runqueue which had its rq->util to be at
>> 100%. After the load finishes, the runqueue goes idle. For every
>> scheduler tick, its utilisation decays. But can never become 0.
>>
>> rq->util = rq->avg.runnable_avg_sum/rq->avg.runnable_avg_period
> 
> 
> did you close all of background system services?
> In theory the rq->avg.runnable_avg_sum should be zero if there is no
> task a bit long, otherwise there are some bugs in kernel.

Could you explain why rq->avg.runnable_avg_sum should be zero? What if
some kernel thread ran on this run queue and is now finished? Its
utilisation would be say x.How would that ever drop to 0,even if nothing
ran on it later?

Regards
Preeti U Murthy

 Could you
> check the value under /proc/sched_debug?
> 
> 

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