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

[Jan Kiszka <kiszka@domain.hid>]

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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.

Jan


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