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Old 05-06-2010, 12:33 PM
Bryan Wu
 
Default fsl-imx51: Enabling function tracer and function profiler of the ftrace

On 05/06/2010 05:56 PM, Chase Douglas wrote:
> On Wed, May 5, 2010 at 10:18 PM, AceLan Kao<acelan.kao@canonical.com> wrote:
>> The fsl-imx51 branch doesn't support too much features of the ftrace,
>> including FUNCTION_GRAPH_TRACER, DYNAMIC_FTRACE, MMIOTRACE
>> Do you think is there any other useful options should be enabled?
>> I can try to see if they're supported in the fsl-imx51 branch.
>
> if DYNAMIC_FTRACE is not supported, then we don't want any of this
> enabled by default. DYNAMIC_FTRACE is the magic that lets you turn
> tracing on and off at runtime. If you can't do that, then everything
> will be traced all the time. This would hurt performance.
>
> It looks like this could be resolved soon for ARM though:
> http://thread.gmane.org/gmane.linux.kernel/949812, but I haven't read
> all the replies, and it hasn't landed in Linus' tree nor in Steve
> Rostedt's.
>
> Thus, NACK from me for enabling ftrace on any ARM platform until it
> has DYNAMIC_FTRACE support. Of course, we can still make debug kernels
> for specific testing, we just can't enable it for a release kernel.
>
> -- Chase
>

OK, got it. Since DYNAMIC_FTRACE is not fully functional in ARM, enabling FTRACE
configs default for fsl-imx51 is not what we want.

I will keep tracking the upstream status about that.

AceLan, Thanks for file this bug and post this patch anyway.
But another patch which fixes the ftrace compiling bug should go into our Lucid
and Maverick tree, because we still need it when we enable FTRACE configs for
our own debugging.

Cheers,
--
Bryan Wu <bryan.wu@canonical.com>
Kernel Developer +86.138-1617-6545 Mobile
Ubuntu Kernel Team | Hardware Enablement Team
Canonical Ltd. www.canonical.com
Ubuntu - Linux for human beings | www.ubuntu.com

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