Messages in this thread | | | Subject | Re: rt20 scheduling latency testcase and failure data | From | Sébastien Dugué <> | Date | Mon, 15 May 2006 13:15:46 +0200 |
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On Fri, 2006-05-12 at 19:24 -0700, Darren Hart wrote: > I have been noticing unexpected intermittant large latencies. I wrote the > attached test case to try and capture some information on them. The librt.h > file contains convenience functions I use for writing other tests as well, so > much of it is irrelevant, but the test case itself is pretty clear I believe. > > The test case emulates a periodic thread that wakes up on time%PERIOD=0, so > rather than sleeping the same amount of time each round, it checks now > against the start of its next period and sleeps for that length of time. > Every so often it will miss it's period, I've captured that data and included > a few of the interesting bits below. The results are from a run with a > period of 5ms, although I have seen them with periods as high as 17ms. The > system was under heavy network load for some of the time, but not all. >
Hi Darren,
FWIW:
I've been running you test program on my box under a stress-kernel load and did not observe any failure as you describe, not even a max latency overshooting the 100 us limit (max latencies in the 60~70 us).
I even went to decrease PERIOD to 1 ms and still no failure.
I'm running rt20 with the futex priority based wakeup patch on a dual 2.8 GHz HT Xeon box. All hardirq and softirq threads are at their default priority.
How do you generate the network load you mention? Maybe I could try at least with the same load you're using.
Sébastien.
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