[Xenomai-help] Strange issue : high latency for kernel task when a user task is stop

[Xenomai-help] Strange issue : high latency for kernel task when a user task is stop

[Gilles FRITZ]

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Hi,

I use Xenomai since not very long, but I have seen a strange behavior : when
I stop a user-space task, my in-kernel task have a latency of about 500µs.

I have observed that on Xenomai 2.4.8 and 2.3.4, on kernel 2.6.25.19 and
2.6.28.9.

To observe that, I launch two latency test : one in user-space and the
second in kernel-space
latency -p 50 -t 1
latency -p 70

When I stop the second latency (in user-space), I can observe a latency of
at least 500ms in the in-kernel task.

I do not know if this is normal or not.

Have you an explanation for that?

-- 
Regards,
Gilles FRITZ



-- 
Cordialement,
Gilles FRITZ

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Re: [Xenomai-help] Strange issue : high latency for kernel task when a user task is stop

[Gilles Chanteperdrix]

Gilles FRITZ wrote:
> Hi,
> 
> I use Xenomai since not very long, but I have seen a strange behavior : when
> I stop a user-space task, my in-kernel task have a latency of about 500µs.
> 
> I have observed that on Xenomai 2.4.8 and 2.3.4, on kernel 2.6.25.19 and
> 2.6.28.9.
> 
> To observe that, I launch two latency test : one in user-space and the
> second in kernel-space
> latency -p 50 -t 1
> latency -p 70
> 
> When I stop the second latency (in user-space), I can observe a latency of
> at least 500ms in the in-kernel task.
> 
> I do not know if this is normal or not.
> 
> Have you an explanation for that?

I do not think we have but:
- 50us and 70us are a bit short periods depending on the platform
(though it should not change anything to use larger periods), and you
did not tell us on what platform you are running xenomai
- the I-pipe patch proposes an option, the I-pipe tracer, which will
tell you exactly what happens during these 500us.

-- 
					    Gilles.