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

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Date:	Tue, 20 Apr 2010 00:04:39 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
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 Mon, Apr 19, 2010 at 05:37:54PM -0400, Steven Rostedt wrote:
> On Mon, 2010-04-19 at 23:29 +0200, Frederic Weisbecker wrote:
> 
> > The problem with having triggers defined in the filter file is that
> > you couldn't set a normal filter plus a trigger.
> > 
> > That said a filter itself could be a trigger.
> > 
> > if (cond) filter
> > 
> > This is going to break some ABI though.
> > 
> > In fact having one file per trigger type is going to make the
> > things much easier if you don't want to encumber with syntax parsing,
> > and just reuse the filtering code as is with very few modification.
> > This is going to be also easier for the users as they don't have to
> > remember the syntax or the available triggers.
> > 
> > Say you are in an event directory:
> > 
> > $ ls triggers/
> > 
> > filter
> > tracing_off
> > tracing_on
> > dump_trace
> > 
> > $ echo "(a == 1 && b == 2)" > tracing_off
> > 
> > So in the above example, you just reuse the filtering code,
> > no need to parse an if or a command.
> > The filter becomes a command. I've listed it in the triggers
> > directory but this just to express the fact it can be treated
> > like whatever trigger command, this is just an implementation
> > POV. In fact we can just keep it in the event directory.
> 
> 
> I like this. Heck, all registered triggers can be shown here.
> 
> # cat event/sched/sched_switch/triggers/tracing_off
> disabled
> 
> Or it can be a filter, or enabled.


Yep, since it would share exatly the same code than filter (as
filter basically becomes a trigger command), it can behave the
same: displaying "none" when there is no filter, or a filter.


> 
> 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.

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