Re: [RFC PATCH 2/2] tracing: add sched_set_prio tracepoint

Mathieu Desnoyers
2016-06-06T19:52:07Z

----- On May 30, 2016, at 9:18 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:

> ----- On May 27, 2016, at 5:16 PM, Julien Desfossez jdesfossez@efficios.com
> wrote:
>
>> This tracepoint allows to keep track of all priority changes made by all
>> sites that can change this value. The impacted system calls are
>> sched_setscheduler, sched_setattr, sched_process_fork and set_user_nice.
>> The priority inheritance mechanism from rt_mutex gets also instrumented
>> with this tracepoint even though there is a dedicated tracepoint for it
>> (sched_pi_setprio).
>>
>> This allows analysis of real-time scheduling delays per thread priority,
>> which cannot be performed accurately if we only trace the priority of
>> the currently scheduled processes.
>>
>> Here is an example of what is output by ftrace when we change the
>> priority of a running process:
>> sys_sched_setscheduler(pid: 1c52, policy: 2, param: 7ffc22e20980)
>> sched_set_prio: comm=burnP6 pid=7250 oldprio=120 newprio=39
>> sys_sched_setscheduler -> 0x0
>> sched_switch: prev_comm=chrt prev_pid=7268 prev_prio=120
>> prev_state=R ==> next_comm=burnP6 next_pid=7250
>> next_prio=39
>>
>> Signed-off-by: Julien Desfossez <jdesfossez@efficios.com>
>
> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Adding Ingo and Peter in CC, considering that it touches to tracing and
the scheduler.

Thanks,

Mathieu

>
>> ---
>> include/trace/events/sched.h | 21 ++++++++++++++++-----
>> kernel/sched/core.c | 1 +
>> 2 files changed, 17 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
>> index 9b90c57..3b83ddb 100644
>> --- a/include/trace/events/sched.h
>> +++ b/include/trace/events/sched.h
>> @@ -407,11 +407,7 @@ DEFINE_EVENT(sched_stat_runtime, sched_stat_runtime,
>> TP_PROTO(struct task_struct *tsk, u64 runtime, u64 vruntime),
>> TP_ARGS(tsk, runtime, vruntime));
>>
>> -/*
>> - * Tracepoint for showing priority inheritance modifying a tasks
>> - * priority.
>> - */
>> -TRACE_EVENT(sched_pi_setprio,
>> +DECLARE_EVENT_CLASS(sched_prio_template,
>>
>> TP_PROTO(struct task_struct *tsk, int newprio),
>>
>> @@ -436,6 +432,21 @@ TRACE_EVENT(sched_pi_setprio,
>> __entry->oldprio, __entry->newprio)
>> );
>>
>> +/*
>> + * Tracepoint for showing priority inheritance modifying a tasks
>> + * priority.
>> + */
>> +DEFINE_EVENT(sched_prio_template, sched_pi_setprio,
>> + TP_PROTO(struct task_struct *tsk, int newprio),
>> + TP_ARGS(tsk, newprio));
>> +
>> +/*
>> + * Tracepoint for priority changes of a task.
>> + */
>> +DEFINE_EVENT(sched_prio_template, sched_set_prio,
>> + TP_PROTO(struct task_struct *tsk, int newprio),
>> + TP_ARGS(tsk, newprio));
>> +
>> #ifdef CONFIG_DETECT_HUNG_TASK
>> TRACE_EVENT(sched_process_hang,
>> TP_PROTO(struct task_struct *tsk),
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 6946b8f..45fbaab 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -2232,6 +2232,7 @@ int sysctl_schedstats(struct ctl_table *table, int write,
>>
>> static void sched_set_prio(struct task_struct *p, int prio)
>> {
>> + trace_sched_set_prio(p, prio);
>> p->prio = prio;
>> }
>>
>> --
>> 1.9.1
>
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

--
Mathieu Desnoyers
EfficiOS Inc.