linux-kernel - Re: Anyone working on ftrace function graph support on ARM?

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Date:	Wed, 25 Mar 2009 09:41:13 -0700
From:	Tim Bird <tim.bird@...sony.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Abhishek Sagar <sagar.abhishek@...il.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.arm.linux.org.uk>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: Anyone working on ftrace function graph support on ARM?

Ingo Molnar wrote:
> Unwinding is not realistic or desired for the function tracer - it 
> runs in every kernel function so performance is paramount.
> 
> So, if i understood you correctly, an OABI_COMPAT and FRAME_POINTERS 
> dependency has to be added to the ARM HAVE_FUNCTION_GRAPH_TRACER 
> Kconfig rule.

This, unfortunately, is a problem for me.  All my ARM
projects are now using EABI.  If the unwinding looks like
it has too much overhead, I'll do some research on the
-finstrument-functions (__cyg_profile_func_enter/exit) approach.

I'm not sure, however, if it's possible to integrate this with
the dynamic tracing mechanisms, though.  So something may have
to give to get this supported on ARM.
 -- Tim

=============================
Tim Bird
Architecture Group Chair, CE Linux Forum
Senior Staff Engineer, Sony Corporation of America
=============================

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