Re: [PATCH] sched/rt: Add pid and comm when RT throttling activated

["Yajun Deng" <yajun.deng@linux.dev>]

December 10, 2022 5:36 AM, "Steven Rostedt" <rostedt@goodmis.org> wrote:

> On Tue, 6 Dec 2022 16:36:41 +0800
> Yajun Deng <yajun.deng@linux.dev> wrote:
> 
>> It is difficult to know which process consumes time when RT throttling
>> activated.
>> 
>> So add pid and comm for this case.
> 
> Unfortunately, that only shows the process that "broke the camel's
> back"[1]. The things is, it is the amount of time *all* RT tasks use to
> trigger throttling. You are only printing the task that the throttling
> occurred on.
> 
> Try running https://rostedt.org/code/migrate.c . It will create a bunch of
> RT tasks, and they all will throttle once it hits 950ms ever second.
> 
> trace-cmd record -e sched_switch ./migrate
> kernelshark
> 
> Then plot all the migrate tasks.
> 
> The above will demonstrate it very well.

Thanks for your patient answer, I'll test it.

> 
> -- Steve
> 
> [1] https://en.wikipedia.org/wiki/Straw_that_broke_the_camel's_back
> 
>> Signed-off-by: Yajun Deng <yajun.deng@linux.dev>
>> ---
>> kernel/sched/rt.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>> 
>> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>> index ed2a47e4ddae..1f267ab1b59a 100644
>> --- a/kernel/sched/rt.c
>> +++ b/kernel/sched/rt.c
>> @@ -1012,6 +1012,7 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
>> 
>> if (rt_rq->rt_time > runtime) {
>> struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
>> + struct task_struct *curr = rq_of_rt_rq(rt_rq)->curr;
>> 
>> /*
>> * Don't actually throttle groups that have no runtime assigned
>> @@ -1019,7 +1020,8 @@ 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("pid: %d, comm: %s, sched: RT throttling activated\n",
>> + curr->pid, curr->comm);
>> } else {
>> /*
>> * In case we did anyway, make it go away,