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

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Message-ID: <4BCCBF6D.3030105@am.sony.com>
Date:	Mon, 19 Apr 2010 13:39:09 -0700
From:	Tim Bird <tim.bird@...sony.com>
To:	"rostedt@...dmis.org" <rostedt@...dmis.org>
CC:	Tom Zanussi <tzanussi@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	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 04/19/2010 01:04 PM, Steven Rostedt wrote:
> Hi Tom,
> 
> Could you add a way to do a call to tracing_on() or tracing_off() via
> the filters. I would like to do something like:
> 
> 
> echo 'if (pid == 1234) traceoff' > events/sched/sched_wakeup/filter
> 
> Where, if the sched_wakeup event is hit with pid == 1234 it will turn
> tracing off.

Just a comment on the nomenclature.  In KFT I called
things like this "triggers".  I'm not sure what other
tracing systems call them.  I'm a little worried about
overloading the filtering abstraction with trigger
semantics.  (I like the idea of triggers, but it might
be better to control them with another pseudo-file for
clarity.)

I suppose both are a form of conditional execution.
Filtering has an implicit action of either 'trace this'
or 'don't trace this', while triggering usually has
an action, often explicit, to start or stop tracing.
However, since they both use the conditional testing,
it might be a pain to reproduce this code for a different
pseudo-file.

Just my 2 cents.
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Network Entertainment
=============================

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