Re: [Xenomai-help] Cyclictest

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

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Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Gilles Chanteperdrix wrote:
>>
>>> Jan Kiszka wrote:
>>>
>>>> Perrine Martignoni wrote:
>>>>
>>>>
>>>>> Ok. I'll do this.
>>>>>
>>>>> But I don't understand why the same application compiled without any links
>>>>> with Xenomai give different results if there is Xenomai in the kernel.
>>>> [Looking at your numbers again] Hmm, maybe some rounding issue of ticks
>>>> due to whatever side-effect of I-pipe. We would first of all need the
>>>> usual set of information (.config, involved versions) and also
>>>> /sys/devices/system/clocksource/clocksource0/current_clocksource.
>>> Maybe what Perrine is observing is simply the overhead of the I-pipe ?
>>> I mean, Linux is Xenomai idle task, so it is acceptable for Linux
>>> numbers to be a bit worse than when Xenomai is not running.
>>
>> I bit worse is expected. But I think we are seeing 1 or 2 ticks wake-up
>> delays here. As far as I understood, they are not due to Xenomai
>> consuming significant cycles in the background, are they, Perrine?
> 
> What I see is latencies 5us longer. 5us on ARM is almost nothing, keep
> in mind that a simple syscall on ARM already takes 10 us.
> 

T: 0 (  732) P:99 I:   10500 C:    2291 Min:      41 Act:    2281 Avg:    5075 Max:   10224 

vs.

T: 0 (  893) P:99 I:   10000 C:    1756 Min:   13407 Act:   13536 Avg:   13452 Max:   13693 

Thus the _minimum_ and the _average_ wakeup time of a Linux task
increase fairly significant here. That's the point. Given a reasonable
runtime of both test, this /could/ be considered as a regression of a
Xenomai-enabled Linux kernel.

Jan


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