Re: [Xenomai-help] Latencies while ethernet access

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

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Gilles Chanteperdrix wrote:
> CAMUS Benoit wrote:
>> Hi,
>>
>> I'm using Xenomai 2.3.1 with a 2.6.19.2 kernel (from ELDK) on a custom
>> board based on Xscale PXA processor and with smc91c111 ethernet chip. 
>> I did modifications on Linux kernel to port it on board and then just
>> applied Adeos's patch following Xenomai's proceedings.
>> Http and telnet servers are running on and i notice that latencies get
>> really worse while i access any of them (see traces below).
>>
>> I understood that Adeos might avoid that kind of behavior due to its
>> architecture. So i infer that the ethernet driver might access the
>> hardware by-passing Adeos ?
> 
> Despite Adeos architecture, latency with Xenomai is known to depend on
> the non real-time workload, because there are some low-level ressources
> such as busses and processor cache that the real-time and non real-time
> processes need to share.

Such effects can often be analysed with... the latency tracer [1]!

When some hardware interaction shows up right before the delayed timer
(or whatever RT-)IRQ, Xenomai cannot help. But if there is something
else, more fishy going on, you will see long interrupts-off sections,
weird scheduling decisions, etc. Then our job starts again.

Jan

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


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