Re: [Xenomai-help] Latencies due to RT-Socket-CAN register accesses

[Jan Kiszka <jan.kiszka@domain.hid>]

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roland Tollenaar wrote:
>> > I am aware of this. For the current machine I will stick to this.
>> >
>>
>> Then don't complain. :)
> Yes sir!
> :)
> Not complaining really, I think and I hope that the latency of 30us
> average will do nicely for me. Just curious actually.
> 
>> > to be give worse latencies than much slower machines. Are the 2
>> > interrupts causing the latency?
>>
>> Those two increase the latency of code in timed tasks, for sure. The
>> question is if your measurement on the slower machine also included this
>> scenario (timer event + 2 IRQs in a row). This definitely doesn't happen
>> often, and maybe timing on the slower box makes it less likely. Or there
>> is one potential IRQ source more on your fast box (e.g. due to IRQ
>> sharing on the slower one).
>>
>> You see, RT system design on the edge (ie. when hunting a few 10 us) is
>> tricky and not easily portable from box X to box Y.
> 
> Its not possible to determine which IRQ's are responsible for this
> from the trace I presume?
> 

echo 1 > /proc/ipipe/trace/verbose

Then look at the "User Val." reported at "common_interrupt" (see also [1]).

Jan

[1] http://www.xenomai.org/index.php/I-pipe:Tracer


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