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

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Date:	Thu, 10 Jan 2013 11:40:44 +0000
From:	Morten Rasmussen <Morten.Rasmussen@....com>
To:	Alex Shi <alex.shi@...el.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 Sat, Jan 05, 2013 at 08:37:44AM +0000, Alex Shi wrote:
> The cpu's utilization is to measure how busy is the cpu.
>         util = cpu_rq(cpu)->avg.runnable_avg_sum
>                 / cpu_rq(cpu)->avg.runnable_avg_period;
> 
> Since the util is no more than 1, we use its percentage value in later
> caculations. And set the the FULL_UTIL as 99%.
> 
> In later power aware scheduling, we are sensitive for how busy of the
> cpu, not how weight of its load. As to power consuming, it is more
> related with busy time, not the load weight.
> 
> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
>  kernel/sched/debug.c | 1 +
>  kernel/sched/fair.c  | 4 ++++
>  kernel/sched/sched.h | 4 ++++
>  3 files changed, 9 insertions(+)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 2cd3c1b..e4035f7 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -318,6 +318,7 @@ do {									\
>  
>  	P(ttwu_count);
>  	P(ttwu_local);
> +	P(util);
>  
>  #undef P
>  #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?

Morten

>  }
>  
>  /* 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 66b08a1..3c6e803 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 */
>  
> +/* Take as full load, if the cpu percentage util is up to 99 */
> +#define FULL_UTIL	99
> +
>  /*
>   * 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)
> -- 
> 1.7.12
> 
> --
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