linux-kernel - Re: [patch v6 10/21] sched: get rq potential maximum utilization

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Message-ID: <87a9phfgox.fsf@sejong.aot.lge.com>
Date:	Tue, 02 Apr 2013 18:02:54 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	mingo@...hat.com, peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org, arjan@...ux.intel.com, bp@...en8.de,
	pjt@...gle.com, efault@....de, vincent.guittot@...aro.org,
	gregkh@...uxfoundation.org, preeti@...ux.vnet.ibm.com,
	viresh.kumar@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [patch v6 10/21] sched: get rq potential maximum utilization

Hi Alex,

On Sat, 30 Mar 2013 22:34:57 +0800, Alex Shi wrote:
> Since the rt task priority is higher than fair tasks, cfs_rq utilization
> is just the left of rt utilization.
>
> When there are some cfs tasks in queue, the potential utilization may
> be yielded, so mulitiplying cfs task number to get max potential
> utilization of cfs. Then the rq utilization is sum of rt util and cfs
> util.
>
> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
>  kernel/sched/fair.c | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index ae87dab..0feeaee 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3350,6 +3350,22 @@ struct sg_lb_stats {
>  	unsigned int group_util;	/* sum utilization of group */
>  };
>  
> +static unsigned long scale_rt_util(int cpu);
> +
> +static unsigned int max_rq_util(int cpu)
> +{
> +	struct rq *rq = cpu_rq(cpu);
> +	unsigned int rt_util = scale_rt_util(cpu);
> +	unsigned int cfs_util;
> +	unsigned int nr_running;
> +
> +	cfs_util = (FULL_UTIL - rt_util) > rq->util ? rq->util
> +			: (FULL_UTIL - rt_util);
> +	nr_running = rq->nr_running ? rq->nr_running : 1;

This can be cleaned up with proper min/max().

> +
> +	return rt_util + cfs_util * nr_running;

Should this nr_running consider tasks in cfs_rq only?  Also it seems
there's no upper bound so that it can possibly exceed FULL_UTIL.

Thanks,
Namhyung

> +}
> +
>  /*
>   * sched_balance_self: balance the current task (running on cpu) in domains
>   * that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
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