linux-kernel - Re: [PATCH 1/1] ftrace: fix dynamic ftrace filter reset issue

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Date:	Sat, 24 Mar 2012 09:55:05 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Rajesh Bhagat <rajesh.lnx@...il.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] ftrace: fix dynamic ftrace filter reset issue

On Sat, 2012-03-24 at 09:47 +0530, Rajesh Bhagat wrote:
> Hi Steven,
> 
> Thanks for the reply.
> 
> I was wondering, why would a user reset the trace __explicitly__
> without even using it.
> That is why i created a patch for it.
> 
> >> /debug/tracing # echo function > current_tracer
      ^
      |
   user starts using tracer

> >> /debug/tracing # cat trace <------ Not performed
> >> /debug/tracing # echo schedule > set_ftrace_filter
> >> /debug/tracing # echo function > current_trace
> >> /debug/tracing # cat trace <------- Only this is performed

Why the first "echo function"? That means you just started using the
tracer. You can (and should) do:

	# echo schedule > set_ftrace_filter
	# echo function > current_tracer

This IIRC is the documented way of using it.

That said, I may consider taking the patch, as another way of resetting
the tracer. I have to see what workflows it will affect first.

-- Steve


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