linux-kernel - Re: [PATCH] sched/rt: Print curr when RT throttling activated

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Date:   Thu, 3 Dec 2020 09:39:56 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Xianting Tian <tian.xianting@....com>
Cc:     <mingo@...hat.com>, <peterz@...radead.org>,
        <juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
        <dietmar.eggemann@....com>, <bsegall@...gle.com>,
        <mgorman@...e.de>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/rt: Print curr when RT throttling activated

On Thu, 3 Dec 2020 15:51:29 +0800
Xianting Tian <tian.xianting@....com> wrote:

> We may meet the issue, that one RT thread occupied the cpu by 950ms/1s,
> The RT thread maybe is a business thread or other unknown thread.
> 
> Currently, it only outputs the print "sched: RT throttling activated"
> when RT throttling happen. It is hard to know what is the RT thread,
> For further analysis, we need add more prints.
> 
> This patch is to print current RT task when RT throttling activated,
> It help us to know what is the RT thread in the first time.

I think this can be useful information to include.

Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> 
> Signed-off-by: Xianting Tian <tian.xianting@....com>
> ---
>  kernel/sched/rt.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index f215eea6a..8913f38cb 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -946,7 +946,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
>  	return rt_task_of(rt_se)->prio;
>  }
>  
> -static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
> +static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, struct task_struct *curr)
>  {
>  	u64 runtime = sched_rt_runtime(rt_rq);
>  
> @@ -970,7 +970,8 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
>  		 */
>  		if (likely(rt_b->rt_runtime)) {
>  			rt_rq->rt_throttled = 1;
> -			printk_deferred_once("sched: RT throttling activated\n");
> +			printk_deferred_once("sched: RT throttling activated (curr: pid %d, comm %s)\n",
> +						curr->pid, curr->comm);
>  		} else {
>  			/*
>  			 * In case we did anyway, make it go away,
> @@ -1026,7 +1027,7 @@ static void update_curr_rt(struct rq *rq)
>  		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
>  			raw_spin_lock(&rt_rq->rt_runtime_lock);
>  			rt_rq->rt_time += delta_exec;
> -			if (sched_rt_runtime_exceeded(rt_rq))
> +			if (sched_rt_runtime_exceeded(rt_rq, curr))
>  				resched_curr(rq);
>  			raw_spin_unlock(&rt_rq->rt_runtime_lock);
>  		}