Re: [PATCH][V2] sched/rt: Print curr when RT throttling activated

[Alexandru Ardelean]

On Tue, May 16, 2023 at 3:22 PM Alexandru Ardelean <alex@xxxxxxxxxxx> wrote:
>
> From: Xianting Tian <tian.xianting@xxxxxxx>
>
> 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.
>

Adding Greg on this patch, since it 's been a while.
And also: ping :)

> Tested-by: Alexandru Ardelean <alex@xxxxxxxxxxx>
> Signed-off-by: Xianting Tian <tian.xianting@xxxxxxx>
> ---
>
> Initial patch submission:
>   https://lore.kernel.org/all/f3265adc26d4416dacf157f61fa60ad6@xxxxxxx/T/
>
> We've been having some issues of our own with some applications + some RT
> configuration == some threads endded up taking too much CPU time.
> This patch came in quite in handy to see in logs which thread is more
> problematic.
>
> We've applied this patch onto a 5.10.116 tree. It did need a bit of
> re-applying since some context has changed since the initial version (hence
> the V2 tag).
> Since 5.10.116 (where we used it), it applied nicely to the latest/current
> linux-next tree (hence the Tested-by tag).
>
> It would be nice to apply this to the mainline kernel and have this handy.
>
>  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 00e0e5074115..44b161e42733 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -995,7 +995,7 @@ 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);
>
> @@ -1019,7 +1019,8 @@ 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,
> @@ -1074,7 +1075,7 @@ 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;
> -                       exceeded = sched_rt_runtime_exceeded(rt_rq);
> +                       exceeded = sched_rt_runtime_exceeded(rt_rq, curr);
>                         if (exceeded)
>                                 resched_curr(rq);
>                         raw_spin_unlock(&rt_rq->rt_runtime_lock);
> --
> 2.40.1
>