alamo hwuang wrote: > Hi , I am using the xenomai to build the paltform and getting a latency test > results. > > RTT| 00:00:01 (periodic user-mode task, 100 us period, priority 99) > RTH|----lat min|----lat avg|----lat max|-overrun|---msw|---lat best|--lat > worst > RTD| -2.362| -2.179| 0.017| 0| 0| -2.428| > 3.189 > > How can I read the meaning of those results ? > > and Are those results are correct???
It depends on what platform you are running. But from the results you get, you are probably running latency on x86_64, without any load. The results you get doing so are probably meaningless. If you wonder about the negative latencies, they simply mean that your system is not calibrated correctly. The latency tool measures the wake up latency of user-space/kernel-space task by using the timer services, so, in fact, the timer wake-up latency. However, in order to compensate for the constant overhead of the thread wake-up path, the timer services anticipate. So, when you ask for a thread to be woken up at time T, the timer will tick at T - compensation So, that when the task is finally woken up, it will appear to have woken up at a time close to T. This anticipation may be chosen with /proc/xenomai/latency A system running Xenomai has to be calibrated, an anticipation has to be chosen according to what you want, and what your system can do. So, you should do: echo 0 > /proc/xenomai/latency This will disable the anticipation. Then run latency under load for a long time. Then according to the results given by the test, and what you need for your application, echo the value you choose to /proc/xenomai/latency. The value the latency test will give you with a null anticipation is the scheduling latency. Xenomai pick some default value for this anticipations which comes from boards on which we test it, which can result on negative latencies on other boards. > > what is the max size of a xenomai task stack size? Xenomai relies on the glibc to create threads. So, the rule for stack sizes are no different for a Xenomai task than for any non real-time task on the system. But beware of mlockall (see the TROUBLESHOOTING guide on this subject). Please note that for such questions, the xenomai-help mailing list is more appropriate. -- Gilles. _______________________________________________ Xenomai-core mailing list Xenomaifirstname.lastname@example.org https://mail.gna.org/listinfo/xenomai-core