2022-12-06 09:09:49

by Yajun Deng

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

It is difficult to know which process consumes time when RT throttling
activated.

So add pid and comm for this case.

Signed-off-by: Yajun Deng <[email protected]>
---
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,
--
2.25.1

2022-12-09 22:15:18

by Steven Rostedt

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

On Tue, 6 Dec 2022 16:36:41 +0800
Yajun Deng <[email protected]> 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.

-- Steve


[1] https://en.wikipedia.org/wiki/Straw_that_broke_the_camel%27s_back

> Signed-off-by: Yajun Deng <[email protected]>
> ---
> 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,

2022-12-12 02:36:15

by Yajun Deng

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

December 10, 2022 5:36 AM, "Steven Rostedt" <[email protected]> wrote:

> On Tue, 6 Dec 2022 16:36:41 +0800
> Yajun Deng <[email protected]> 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 <[email protected]>
>> ---
>> 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,