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

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Message-ID: <1271713074.10448.101.camel@gandalf.stny.rr.com>
Date:	Mon, 19 Apr 2010 17:37:54 -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 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.

This could also allow a user to do:

echo "(a > 100)" > tracing_on
echo "(a < 100)" > tracing_off

-- Steve



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