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Big jitter in packet round-trip time (eth0)


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Dear Colleagues,


I'm trying to implement a solution for data exchange between a host and Power PMAC with a dual core ARM processor using udp protocol. I would like to reach stable <1 ms exchange times. But what I'm concerned is a big jitter of packet round-trip time. For comparison purpose I measured exchange times with my old box on Atom processor and I observed much better and stable statistics.


I tried to ping my power pmac to gather some latency statistics on eth0 interface. I observe latencies from ~200 us up to 2-3 ms (up to 10x times difference). Such jitter in latencies is not desirable for my project.


Ping statistics: min/avg/max/mdev = 0.088/0.454/1.962/0.311 ms


I also tried to measure round-trip times with my custom UDP server and client. The times were like those for ping. PMAC is not configured, without any servo connected. CPUs are not loaded. My current thought that the problem is in eth0 network card. I found some other messages like mine but I still haven't found a solution for my case.


Could you please advice what should be investigated or configured to improve the stability of round-trip times?


Any ideas are welcome,

Thank you in advance!

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I found that the problem is originated in powerpmac service. Well, it's expected :) If to stop the service - ping is ~0.160 ms with the minimum jitter, RT task timings (in the primary mode) are kept very precisely (jitter - tens of microseconds). So, the next question - how to configure the powerpmac service for better cpu utilization?
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