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

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- 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>

> ---
> 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