linux-kernel - Re: [PATCH] tracing/function-graph-tracer: make set_graph

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Message-ID: <20090220104004.GC28581@elte.hu>
Date:	Fri, 20 Feb 2009 11:40:04 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing/function-graph-tracer: make set_graph_function
	file support ftrace regex


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> Impact: trace only functions matching a pattern
> 
> The set_graph_function file let one to trace only one or several
> chosen functions and follow all their code flow.
> 
> Currently, only a constant function name is allowed so this patch
> allows the ftrace_regex functions:
> 
> _ matches all functions that end with "name":
>   echo *name > set_graph_function
> 
> _ matches all functions that begin with "name":
>   echo name* > set_graph_function
> 
> _ matches all functions that contains "name":
>   echo *name* > set_graph_function
> 
> Example:
> 
> echo mutex* > set_graph_function
> 
>  0)               |  mutex_lock_nested() {
>  0)   0.563 us    |    __might_sleep();
>  0)   2.072 us    |  }
>  0)               |  mutex_unlock() {
>  0)   1.036 us    |    __mutex_unlock_slowpath();
>  0)   2.433 us    |  }
>  0)               |  mutex_unlock() {
>  0)   0.691 us    |    __mutex_unlock_slowpath();
>  0)   1.787 us    |  }
>  0)               |  mutex_lock_interruptible_nested() {
>  0)   0.548 us    |    __might_sleep();
>  0)   1.945 us    |  }
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> ---
>  kernel/trace/ftrace.c |   56 +++++++++++++++++++++++++++++++++---------------
>  1 files changed, 38 insertions(+), 18 deletions(-)

Applied, thanks Frederic!

I'm wondering about the following: the whole set_graph_function 
method is limited (to FTRACE_GRAPH_MAX_FUNCS, 32 entries), is 
not scalable (we walk the array of functions at every function 
trace point), has a separate API, etc.

Wouldnt we off better with a good, generic function attributes 
hash, and an extension to the generic regexp parser to enable 
the setting of those attributes? One such attribute could be the 
'expand child function'

	Ingo
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