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

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Date:	Wed, 20 Feb 2013 22:33:57 +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 05:30 PM, Peter Zijlstra wrote:
> On Mon, 2013-02-18 at 13:07 +0800, Alex Shi wrote:
> 
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index fcdb21f..b9a34ab 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;
>>  }
>>  
>>  /* Add the load generated by se into cfs_rq's child load-average */
>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
>> index 7a19792..ac1e107 100644
>> --- a/kernel/sched/sched.h
>> +++ b/kernel/sched/sched.h
>> @@ -350,6 +350,9 @@ extern struct root_domain def_root_domain;
>>  
>>  #endif /* CONFIG_SMP */
>>  
>> +/* the percentage full cpu utilization */
>> +#define FULL_UTIL	100
> 
> There's generally a better value than 100 when using computers.. seeing
> how 100 is 64+32+4.

I didn't find a good example for this. and no idea of your suggestion,
would you like to explain a bit more?

> 
>> +
>>  /*
>>   * This is the main, per-CPU runqueue data structure.
>>   *
>> @@ -481,6 +484,7 @@ struct rq {
>>  #endif
>>  
>>  	struct sched_avg avg;
>> +	unsigned int util;
>>  };
>>  
>>  static inline int cpu_of(struct rq *rq)
> 
> 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?
> 


-- 
Thanks
    Alex
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