linux-kernel - Re: request to add trace off and trace on with events

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Date:	Mon, 19 Apr 2010 19:59:26 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Tim Bird <tim.bird@...sony.com>, Tom Zanussi <tzanussi@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Chase Douglas <chase.douglas@...onical.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: request to add trace off and trace on with events

On Tue, 2010-04-20 at 01:04 +0200, Frederic Weisbecker wrote:

> > # ls event/sched/sched_switch/triggers/tracing_off
> > filter   enable
> > 
> > ?
> 
> 
> That would be perhaps an overkill.

Perhaps, but I was also thinking of having triggers in the system level.
That way all events below it can trigger.

> Having a filter inside means it's on, otherwise it's off.
> 
> 
> 
> > 
> > > 
> > > > 
> > > > This could also allow a user to do:
> > > > 
> > > > echo "(a > 100)" > tracing_on
> > > > echo "(a < 100)" > tracing_off
> > > 
> > > 
> > > Yeah :)
> > > But if the scope of the "tracing off" is only for this event, then
> > > rather use:
> > > 
> > > echo "(a < 100)" > filter
> > > 
> > > You could have tracing_off/on that have this event scope and
> > > tracing_off/on_all for a global tracing scope.
> > 
> > The two are not equivalent. In fact, just enabling a trigger does not
> > mean that the event itself will be traced.
> 
> 
> Yeah, the enable file would first need to be activated before any
> trigger to take effect on the event, just like filters.
> 
> In fact I was thinking of tracing_on/tracing_off as kinds of
> local pause/resume.
> 
> And tracing_on_global/tracing_off_global would act like what does
> /debug/tracing/tracing_on: something that disables every tracing.
> 
> But of course, before any of these conditional triggers to be
> evaluated, you need to enable the corresponding event.

We could have a "trace_event_on" and "trace_event_off" trigger that only
enables the event when hit.

Actually, we can have these triggers enable other events, or make
dynamic triggers:

echo "enable_sched_switch" > events/sched/sched_wakeup/trigger/activate

or something similar.

-- Steve



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