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

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Date:	Tue, 2 Apr 2013 16:38:51 +0200
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Alex Shi <alex.shi@...el.com>
Cc:	"mingo@...hat.com" <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Borislav Petkov <bp@...en8.de>, Paul Turner <pjt@...gle.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>, gregkh@...uxfoundation.org,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [patch v6 10/21] sched: get rq potential maximum utilization

On 30 March 2013 15:34, Alex Shi <alex.shi@...el.com> 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);

rt_util and rq->util don't use the same computation algorithm so the
results are hardly comparable or addable. In addition, some RT tasks
can have impacted the rq->util, so they will be accounted in both
side.

Vincent

> +       nr_running = rq->nr_running ? rq->nr_running : 1;
> +
> +       return rt_util + cfs_util * nr_running;
> +}
> +
>  /*
>   * 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
> --
> 1.7.12
>
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