Re: [Xenomai-core] Latencies for the Freescale i.MX21/CSB535FS

[Philippe Gerum <rpm@xenomai.org>]

Jan Kiszka wrote:
> ROSSIER Daniel wrote:
> 
>>>I'd say that the most efficient way to reduce those latencies would
>>>require to first identify the source of the 40+ us spot observed with
>>>the -t2 form on an idle system. For that, I'm convinced that porting the
>>>I-pipe tracer to ARM would be the best option, since this tool would be
>>>of great help there.
>>>
>>
>>Thanks for the hint; we will spend some time on the tracer in the coming days. We keep you informed.
>>
> 
> 
> Cool, tracing also for ARM!
> 
> 
>>>This port basically requires 1) to code the mcount() routine supporting
>>>gcc's -pg option, 2) to solve early boot issues so that mcount() does
>>>not attempt to trace anything while the memory environment has not been
>>>fully set up. The rest is pretty generic.
>>>
> 
> 
> Regarding a mcount() implementation and other details, the original
> tracer effort by Ingo Molnar may give useful hints (at least it did for me):
> 
> http://people.redhat.com/mingo/latency-tracing-patches/
> 
> I remember the ARM part not being that simple as x86. I think this was
> also due to lacking stack unwinding support on that arch.
> 

There's a said to be working replacement for __builtin_return_address 
provided by mingo's patch.
http://people.redhat.com/mingo/latency-tracing-patches/patches/latency-tracing.patch

-- 

Philippe.