Johan Borkhuis wrote:
> When running multiple threads within this program (without load) the
> values range from -5 usec to +5 usec, with an average of around 0 usec.
> But with more RT tasks I see a very high latency once in a while (over
> 400 usec).
>
> Below is the example of such a test run with 10 threads/tasks:
> T: 0 ( 1305) P:80 I:1000 O: 0 Min: -2.404 Avg: -0.001 Max: 1.873
> T: 1 ( 1306) P:79 I:1000 O: 0 Min: -3.052 Avg: -0.001 Max: 1.584
> T: 2 ( 1307) P:78 I:1000 O: 0 Min: -5.694 Avg: 0.000 Max: 18.282
> T: 3 ( 1308) P:77 I:1000 O: 0 Min: -5.166 Avg: 0.046 Max: 479.782
> T: 4 ( 1309) P:76 I:1000 O: 0 Min: -2.595 Avg: 0.036 Max: 368.310
> T: 5 ( 1310) P:75 I:1000 O: 0 Min: -1.731 Avg: -0.001 Max: 1.633
> T: 6 ( 1311) P:74 I:1000 O: 0 Min: -481.273 Avg: -0.001 Max: 490.352
> T: 7 ( 1312) P:73 I:1000 O: 0 Min: -273.947 Avg: -0.001 Max: 277.717
> T: 8 ( 1313) P:72 I:1000 O: 0 Min: -47.016 Avg: -0.001 Max: 45.789
> T: 9 ( 1314) P:71 I:1000 O: 0 Min: -22.968 Avg: -0.001 Max: 29.572
> (P=Priority, I=interval, O=overruns)
>
> When looking at the detailed information, I see that the latencies occur
> when a higher priority task is ending. Is there some specific reason for
> this, or is there some kind of configuration problem with my setup?
Let us suppose that the timers of task 0 and task 2 occur at the same
time. task 2 will have to wait for task 0 to finish its printing job or
for task 0 to reach a suspension point before being able to run. If this
is the reason of the latencies you are observing, disabling root thread
priority coupling should improve the situation.
--
Gilles Chanteperdrix
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