linux-kernel - Re: [PATCH v2] tg: show the sum wait time of an task group

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Date:   Tue, 17 Jul 2018 11:28:40 +0800
From:   王贇 <yun.wang@...ux.alibaba.com>
To:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] tg: show the sum wait time of an task group

Hi, folks

On 2018/7/4 上午11:27, 王贇 wrote:
> Although we can rely on cpuacct to present the cpu usage of task
> group, it is hard to tell how intense the competition is between
> these groups on cpu resources.
> 
> Monitoring the wait time of each process or sched_debug could cost
> too much, and there is no good way to accurately represent the
> conflict with these info, we need the wait time on group dimension.
> 
> Thus we introduced group's wait_sum represent the conflict between
> task groups, which is simply sum the wait time of group's cfs_rq.
> 
> The 'cpu.stat' is modified to show the statistic, like:
> 
>    nr_periods 0
>    nr_throttled 0
>    throttled_time 0
>    wait_sum 2035098795584
> 
> Now we can monitor the changing on wait_sum to tell how suffering
> a task group is in the fight of cpu resources.
> 
> For example:
>    (wait_sum - last_wait_sum) * 100 / (nr_cpu * period_ns) == X%
> 
> means the task group paid X percentage of period on waiting
> for the cpu.

Any comments please?

Regards,
Michael Wang


> 
> Signed-off-by: Michael Wang <yun.wang@...ux.alibaba.com>
> ---
> 
> Since v1:
>    Use schedstat_val to avoid compile error
>    Check and skip root_task_group
> 
>   kernel/sched/core.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 78d8fac..80ab995 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6781,6 +6781,8 @@ static int __cfs_schedulable(struct task_group *tg, u64 period, u64 quota)
> 
>   static int cpu_cfs_stat_show(struct seq_file *sf, void *v)
>   {
> +    int i;
> +    u64 ws = 0;
>       struct task_group *tg = css_tg(seq_css(sf));
>       struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
> 
> @@ -6788,6 +6790,12 @@ static int cpu_cfs_stat_show(struct seq_file *sf, void *v)
>       seq_printf(sf, "nr_throttled %d\n", cfs_b->nr_throttled);
>       seq_printf(sf, "throttled_time %llu\n", cfs_b->throttled_time);
> 
> +    if (schedstat_enabled() && tg != &root_task_group) {
> +        for_each_possible_cpu(i)
> +            ws += schedstat_val(tg->se[i]->statistics.wait_sum);
> +        seq_printf(sf, "wait_sum %llu\n", ws);
> +    }
> +
>       return 0;
>   }
>   #endif /* CONFIG_CFS_BANDWIDTH */