linux-kernel - Re: [patch v5 06/15] sched: log the cpu utilization at rq

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Message-ID: <514C1B23.20701@intel.com>
Date:	Fri, 22 Mar 2013 16:49:39 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	torvalds@...ux-foundation.org, mingo@...hat.com,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	arjan@...ux.intel.com, bp@...en8.de, pjt@...gle.com,
	namhyung@...nel.org, efault@....de, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org,
	morten.rasmussen@....com
Subject: Re: [patch v5 06/15] sched: log the cpu utilization at rq

On 02/20/2013 11:22 PM, Peter Zijlstra wrote:
> On Wed, 2013-02-20 at 22:33 +0800, Alex Shi wrote:
>>> You don't actually compute the rq utilization, you only compute the
>>> utilization as per the fair class, so if there's significant RT
>> activity
>>> it'll think the cpu is under-utilized, whihc I think will result in
>> the
>>> wrong thing.
>>
>> yes. A bit complicit to resolve this. Any suggestions on this, guys?
> 
> Shouldn't be too hard seeing as we already track cpu utilization for !
> fair usage; see rq::rt_avg and scale_rt_power.
> 

Hi Peter,

rt_avg will be accumulated the irq time and steal time in
update_rq_clock_task(), if CONFIG_IRQ_TIME_ACCOUNTING or
CONFIG_IRQ_TIME_ACCOUNTING defined. That cause irq/steal time was double
added into rq utilisation, since normal rq->util already include the irq
time. So we do wrongly judgement to think it is a overload cpu. but it
is not.

To resolve this issue, if is it possible to introduce another member in
rq to describe rt_avg non irq/steal beside the rt_avg? If so, what the
name do you like to use?

-- 
Thanks Alex
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