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SubjectRe: [PATCH v2] tg: show the sum wait time of an task group
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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@linux.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 */

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