From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Mon, 28 Jan 2008 14:46:39 +0100
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: Re: [Xenomai-help] AT91SAM9260 latency
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To: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
Cc: jagarcia@domain.hid, xenomai@xenomai.org

Gilles Chanteperdrix wrote:
> On Jan 28, 2008 2:34 PM, Jan Kiszka <jan.kiszka@domain.hid> wrote:
>> Gilles Chanteperdrix wrote:
>>> ...
>>> The behaviour you get may be due, for instance, to the fact that the
>>> processor goes into some sleep mode when idle and to a wake-up
>>> latency; if you run some load, there is no wake-up latency. It is hard
>>> to say anything. In order to investigate, I would instrument the
>>> kernel to trace the irq masking sections.
>> Don't we have the I-pipe tracer on this platform?
> 
> Unfortunately, the tracer on arm has too much overhead to give
> meaningful results.

Hmm. Unless the system becomes unusable while running the tracer, I
don't see the show-stopper yet. We are looking for an increase of the
latency when triggering a certain event. That should remain measurable
even if the base latency is far higher than usually.

Do you know what makes the tracer so slow? My "lowest-end" experience
with it are based on a 133 MHz Pentium where the tracer doubled the
worst-case latencies, but the results remained useful for spotting long
paths.

Jan

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