linux-kernel - Re: [PATCH 0/5][RFC] [RFC] function profiler

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Date:	Wed, 25 Mar 2009 10:50:24 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Tom Zanussi <tzanussi@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tim Bird <tim.bird@...sony.com>
Subject: Re: [PATCH 0/5][RFC] [RFC] function profiler


* Steven Rostedt <rostedt@...dmis.org> wrote:

> The following patches are RFC, and to discuss is this work would 
> be useful.
> 
> This patch series adds a function profiler hook to the function 
> tracer and function graph tracer. That is, it uses the mcount 
> calls to track the functions being called. Now with the function 
> graph tracer it also keeps track of the times the functions have 
> been executing.
> 
> Note, this is similar to oprofile, but is not a sampling approach, 
> but a true recorder. Of course, by recording every function the 
> overhead compared to oprofile is higher. With the use of dynamic 
> ftrace, you could just trace certain functions, or just a certain 
> module. The flexibility is a bit greater with this profiling.

Also, with the built-in user-defined filter code in the latest 
tracing tree this can also be used to only trace a given PID, or a 
range of PIDs.

Or we can trace preempt-disabled functions only, via this filter 
expression:

  echo 'common_preempt_count != 0' > /debug/tracing/events/ftrace/function/filter

Or (future planned) we can profile functions only taking longer than 
100 microseconds:

  echo 'duration >= 0' > /debug/tracing/events/ftrace/function/filter

There are other possibilities as well.

	Ingo
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