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Subject: Re: [PATCH v2] tg: show the sum wait time of an task group
From:   =?UTF-8?B?546L6LSH?= <yun.wang@linux.alibaba.com>
To:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org
References: <5c4c978d-e8fb-4bcb-b942-3c6d3dcfc13e@linux.alibaba.com>
 <b9e74571-87d0-ef27-3f14-ebd21d72ee15@linux.alibaba.com>
 <ff7dae3b-e5f9-7157-1caa-ff02c6b23dc1@linux.alibaba.com>
Message-ID: <4abd1bae-dc1e-3a13-40d4-c6c73ecc07b1@linux.alibaba.com>
Date:   Tue, 17 Jul 2018 11:28:40 +0800
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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 */