Sometimes a task is executed with wrong frequency...

Hi,

I have a strange problem with a task frequency. But the problem does not 
occur everytime, so it is hard to find the reason.

I'm running a task for EtherCAT communication at 5 KHz, but sometimes 
the frequency is about 300-500 Hz, measuring the interrupt frequency on 
the EtherCAT interface by a DSP and with a scope.

Sometimes it helps to remove all rtai- and EtherCAT-modules and start 
again, sometimes I have to reboot the system.

The Linux kernel frequency is now 250 HZ (CONFIG_HZ_250), first it was 
1000 Hz.

If the frequncy is ok, then the systems keeps it; the longest test was 
about 2 weeks. I run the latency test for two weeks also and it gives 
good results.

I'm using RTAI 4.1, with kernel 3.14.33. It is a Quad Core™ i7 Ivy 
Bridge Processor running at 2,3 GHz (bluePICE 7000 system). I have other 
systems with the same hardware and software configuration, all behave 
the same way.

Is it a known problem?
Or does someone have an idea how to debug this problem?

thanks for help and hints.

regards

   W. Holzke

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