linux-kernel - Re: [PATCH v3 15/22] sched: log the cpu utilization at rq

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Date:	Wed, 16 Jan 2013 13:53:50 +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 15/22] sched: log the cpu utilization at rq

On 01/14/2013 09:59 PM, Morten Rasmussen wrote:
> On Fri, Jan 11, 2013 at 03:30:30AM +0000, Alex Shi wrote:
>> On 01/10/2013 07:40 PM, Morten Rasmussen wrote:
>>>>>  #undef P64
>>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>>>>> index ee015b8..7bfbd69 100644
>>>>> --- a/kernel/sched/fair.c
>>>>> +++ b/kernel/sched/fair.c
>>>>> @@ -1495,8 +1495,12 @@ static void update_cfs_rq_blocked_load(struct cfs_rq *cfs_rq, int force_update)
>>>>>  
>>>>>  static inline void update_rq_runnable_avg(struct rq *rq, int runnable)
>>>>>  {
>>>>> +	u32 period;
>>>>>  	__update_entity_runnable_avg(rq->clock_task, &rq->avg, runnable);
>>>>>  	__update_tg_runnable_avg(&rq->avg, &rq->cfs);
>>>>> +
>>>>> +	period = rq->avg.runnable_avg_period ? rq->avg.runnable_avg_period : 1;
>>>>> +	rq->util = rq->avg.runnable_avg_sum * 100 / period;
>>> The existing tg->runnable_avg and cfs_rq->tg_runnable_contrib variables
>>> both holds
>>> rq->avg.runnable_avg_sum / rq->avg.runnable_avg_period scaled by
>>> NICE_0_LOAD (1024). Why not use one of the existing variables instead of
>>> introducing a new one?
>>
>> we want to a rq variable that reflect the utilization of the cpu, not of
>> the tg
> 
> It is the same thing for the root tg. You use exactly the same variables
> for calculating rq->util as is used to calculate both tg->runnable_avg and
> cfs_rq->tg_runnable_contrib in __update_tg_runnable_avg(). The only
> difference is that you scale by 100 while __update_tg_runnable_avg()
> scale by NICE_0_LOAD.

yes, the root tg->runnable_avg has same meaningful, but normal tg not,
and more important it is hidden by CONFIG_FAIR_GROUP_SCHED,
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