linux-kernel - Re: [PATCH] sched: split sched

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Date:	Wed, 24 Jun 2015 21:05:15 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Cong Wang <cwang@...pensource.com>
Subject: Re: [PATCH] sched: split sched_switch trace event into two

On Wed, 24 Jun 2015 16:19:33 -0700
Cong Wang <xiyou.wangcong@...il.com> wrote:

> For compatibility, the sched_switch event is not touched.

Yes, and sched_out() should not be added.

> 
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> Signed-off-by: Cong Wang <cwang@...pensource.com>
> ---
>  include/trace/events/sched.h | 51 +++++++++++++++++++++++++++++++++++++++++++-
>  kernel/sched/core.c          |  2 ++
>  2 files changed, 52 insertions(+), 1 deletion(-)
> 
> diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
> index d57a575..c31f1e0 100644
> --- a/include/trace/events/sched.h
> +++ b/include/trace/events/sched.h
> @@ -112,8 +112,57 @@ static inline long __trace_sched_switch_state(struct task_struct *p)
>  #endif /* CREATE_TRACE_POINTS */
>  
>  /*
> - * Tracepoint for task switches, performed by the scheduler:
> + * Tracepoints for task switches, performed by the scheduler:
>   */
> +TRACE_EVENT(sched_out,
> +
> +	TP_PROTO(struct task_struct *curr),
> +
> +	TP_ARGS(curr),
> +
> +	TP_STRUCT__entry(
> +		__array(	char,	comm,	TASK_COMM_LEN	)
> +		__field(	int,	prio			)
> +		__field(	long,	state			)
> +	),
> +
> +	TP_fast_assign(
> +		__entry->prio	= curr->prio;
> +		__entry->state	= __trace_sched_switch_state(curr);
> +		memcpy(__entry->comm, curr->comm, TASK_COMM_LEN);
> +	),
> +
> +	TP_printk("comm=%s prio=%d state=%s%s",
> +		__entry->comm, __entry->prio,
> +		__entry->state & (TASK_STATE_MAX-1) ?
> +		  __print_flags(__entry->state & (TASK_STATE_MAX-1), "|",
> +				{ 1, "S"} , { 2, "D" }, { 4, "T" }, { 8, "t" },
> +				{ 16, "Z" }, { 32, "X" }, { 64, "x" },
> +				{ 128, "K" }, { 256, "W" }, { 512, "P" },
> +				{ 1024, "N" }) : "R",
> +		__entry->state & TASK_STATE_MAX ? "+" : "")
> +);
> +
> +TRACE_EVENT(sched_in,
> +
> +	TP_PROTO(struct task_struct *next),
> +
> +	TP_ARGS(next),
> +
> +	TP_STRUCT__entry(
> +		__array(	char,	comm,	TASK_COMM_LEN	)
> +		__field(	int,	prio			)
> +	),
> +
> +	TP_fast_assign(
> +		memcpy(__entry->comm, next->comm, TASK_COMM_LEN);
> +		__entry->prio	= next->prio;
> +	),
> +
> +	TP_printk("comm=%s prio=%d",
> +		__entry->comm, __entry->prio)
> +);
> +
>  TRACE_EVENT(sched_switch,
>  
>  	TP_PROTO(struct task_struct *prev,
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c86935a..681fc50 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2219,6 +2219,7 @@ prepare_task_switch(struct rq *rq, struct task_struct *prev,
>  		    struct task_struct *next)
>  {
>  	trace_sched_switch(prev, next);
> +	trace_sched_out(prev);

Tracepoints are low overhead, but they do take up space. This is a
useless tracepoint. If anything, I'll work on adding an alias or
something. But please don't add a tracepoint next to a tracepoint that
encompasses the data.

>  	sched_info_switch(rq, prev, next);
>  	perf_event_task_sched_out(prev, next);
>  	fire_sched_out_preempt_notifiers(prev, next);
> @@ -2288,6 +2289,7 @@ static struct rq *finish_task_switch(struct task_struct *prev)
>  	}
>  
>  	tick_nohz_task_switch(current);
> +	trace_sched_in(current);

Why not have a:

	sched_switch_post(prev, current);

That way, the hook can be useful for other tools.

-- Steve

>  	return rq;
>  }
>  

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