Re: [Xenomai] i-pipe tracer on in production kernels? (was Re: Altera Cyclone V)

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On 01/11/2014 11:22 AM, Michael Haberler wrote:
> 
> http://www.xenomai.org/index.php/I-pipe:Tracer describes the trace
> API, which could be useful to track down issues
> 
> Q: does enabling the tracer incur significant overhead if compiled in
> but unused, or is it reasonable to leave it on in a production
> kernel?
> 
> if the former, we might have to build/make available a second i-pipe
> tracer enabled kernel to track down issues 'in the field'; if the
> latter, it'd be less build/distribution chores

Normally, with DYNAMIC_FTRACE, there should be a way to reduce the
overhead. Unfortunately, the I-pipe tracer disables DYNAMIC_FTRACE,
because at some point in the past, it did not work (with the I-pipe
tracer) on ARM. We could re-enable DYNAMIC_FTRACE and try and understand
why it does not work (if it still does not work), but that means you
would have to add patches on top of the I-pipe patch, because all I-pipe
patches released for some time, forbid DYNAMIC_FTRACE with the I-pipe
tracer, at least on ARM.

-- 
                                                                Gilles.