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

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Date:	Wed, 20 Feb 2013 10:30:43 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alex Shi <alex.shi@...el.com>
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 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.

> +
>  /*
>   * 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.

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