linux-kernel - Re: [RFC PATCH] tracing: add sched_prio

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Message-ID: <20160706091325.3f9879eb@gandalf.local.home>
Date:	Wed, 6 Jul 2016 09:13:25 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	Julien Desfossez <jdesfossez@...icios.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, daolivei@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] tracing: add sched_prio_update

On Tue, 5 Jul 2016 21:50:34 +0000 (UTC)
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> >   
> >> +
> >> +	TP_PROTO(struct task_struct *tsk),
> >> +
> >> +	TP_ARGS(tsk),
> >> +
> >> +	TP_STRUCT__entry(
> >> +		__array( char,	comm,	TASK_COMM_LEN	)  
> > 
> > I could imagine this being a high frequency tracepoint, especially with
> > a lot of boosting going on. Can we nuke the comm recording and let the
> > userspace tools just hook to the sched_switch tracepoint for that?  
> 
> We can surely do that.
> 
> Just to clarify: currently this tracepoint is *not* hooked on PI boosting,
> as described in the changelog. This tracepoint is about the prio attributes
> set by user-space. The PI boosting temporarily changes the task struct prio
> without updating the associated policy, which seems rather
> implementation-specific and odd to expose.
> 
> Thoughts ?

Ah, you're right, I was thinking it was at boosting. But still, it's a
rather hefty tracepoint (lots of fields), probably want to keep from
adding comm too.

> 
> Thanks,
> 
> Mathieu
> 
> 
> > 
> > -- Steve
> > 
> >   
> >> +		__field( pid_t,	pid			)
> >> +		__field( unsigned int,	policy		)
> >> +		__field( int,	nice			)
> >> +		__field( unsigned int,	rt_priority	)
> >> +		__field( u64,	dl_runtime		)
> >> +		__field( u64,	dl_deadline		)
> >> +		__field( u64,	dl_period		)
> >> +	),
> >> +
> >> +	TP_fast_assign(
> >> +		memcpy(__entry->comm, tsk->comm, TASK_COMM_LEN);
> >> +		__entry->pid		= tsk->pid;
> >> +		__entry->policy		= tsk->policy;
> >> +		__entry->nice		= task_nice(tsk);
> >> +		__entry->rt_priority	= tsk->rt_priority;
> >> +		__entry->dl_runtime	= tsk->dl.dl_runtime;
> >> +		__entry->dl_deadline	= tsk->dl.dl_deadline;
> >> +		__entry->dl_period	= tsk->dl.dl_period;
> >> +	),
> >> +
> >> +	TP_printk("comm=%s pid=%d, policy=%s, nice=%d, rt_priority=%u, "
> >> +			"dl_runtime=%Lu, dl_deadline=%Lu, dl_period=%Lu",
> >> +			__entry->comm, __entry->pid,
> >> +			__print_symbolic(__entry->policy, SCHEDULING_POLICY),
> >> +			__entry->nice, __entry->rt_priority,
> >> +			__entry->dl_runtime, __entry->dl_deadline,
> >> +			__entry->dl_period)
> >> +);
> >>  #endif /* _TRACE_SCHED_H */
> >>  
> >>  /* This part must be outside protection */
> >> diff --git a/kernel/fork.c b/kernel/fork.c
> >> index 7926993..ac4294a 100644
> >> --- a/kernel/fork.c
> >> +++ b/kernel/fork.c
> >> @@ -1773,6 +1773,7 @@ long _do_fork(unsigned long clone_flags,
> >>  		struct pid *pid;
> >>  
> >>  		trace_sched_process_fork(current, p);
> >> +		trace_sched_prio_update(p);

>From the change log:

"It is emitted in the code path of the sched_setscheduler,
 sched_setattr, sched_setparam, nice and the fork system calls. For fork, it is emitted
 after the sched_process_fork tracepoint for timeline consistency and
 because the PID is not yet set when sched_fork() is called."

I'm not convinced this should be needed. I hate adding back to back
tracepoints.

-- Steve


> >>  		pid = get_task_pid(p, PIDTYPE_PID);
> >>  		nr = pid_vnr(pid);
> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> >> index ce83e39..c729425 100644
> >> --- a/kernel/sched/core.c
> >> +++ b/kernel/sched/core.c
> >> @@ -3708,6 +3708,7 @@ void set_user_nice(struct task_struct *p, long nice)
> >>  			resched_curr(rq);
> >>  	}
> >>  out_unlock:
> >> +	trace_sched_prio_update(p);
> >>  	task_rq_unlock(rq, p, &rf);
> >>  }
> >>  EXPORT_SYMBOL(set_user_nice);
> >> @@ -3912,6 +3913,8 @@ static void __setscheduler(struct rq *rq, struct
> >> task_struct *p,
> >>  		p->sched_class = &rt_sched_class;
> >>  	else
> >>  		p->sched_class = &fair_sched_class;
> >> +
> >> +	trace_sched_prio_update(p);
> >>  }
> >>  
> > >  static void  
>