From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Tue, 24 Apr 2007 12:57:19 +0200
From: Wolfgang Grandegger <wg@domain.hid>
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Subject: Re: [Xenomai-help] Latencies due to RT-Socket-CAN register accesses
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To: roland Tollenaar <rolandtollenaar@domain.hid>
Cc: Xenomai-help@domain.hid, Jan Kiszka <jan.kiszka@domain.hid>

roland Tollenaar wrote:
> Hi
> 
>> Two conclusions:
>>
>>  - You are running your kernel as i586 without TSC support - suboptimal,
>>    costs you a few micros.
> I am aware of this. For the current machine I will stick to this.
> 
> 
>>  - The reported latency perfectly matches the trace, nothing
>>    pathological there. The trace looks like this: Timer fired,
>>    measurement task woken up, two interrupts squeeze themselves between
>>    wakeup and time stamp acquisition. All sane.
> Is it not a bit strange that a machine as fast as this one is supposed
> to be give worse latencies than much slower machines. Are the 2
> interrupts causing the latency?

Yes, what puzzels me is actually the high min latency of more than 24us:

  == Sampling period: 100 us
== Test mode: periodic user-mode task
== All results in microseconds
warming up...
RTT|  00:00:01  (periodic user-mode task, 100 us period, priority 99)
RTH|--lat min|---lat avg|-----lat max|-overrun|----lat best|---lat worst
RTD|   24.304|    35.199|      65.371|       0|      24.304|      65.371

Can the TSC cause such high delays?

And what is the output of "/proc/xenomai/latency"?

Wolfgang.