Messages in this thread | | | Date | Sat, 13 May 2006 11:20:39 +0200 | From | Florian Paul Schmidt <> | Subject | Re: rt20 scheduling latency testcase and failure data |
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On Fri, 12 May 2006 19:24:53 -0700 Darren Hart <dvhltc@us.ibm.com> wrote:
> 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.
[snip]
> I'd appreciate any feedback on the test case, and in particular suggestions on > how I can go about determining where this lost time is being spent.
There's a multitude of ways how you can misconfigure your -rt system :) Tell us more about your setup. Hardware? Full preemption? High resolution timers? Priority setup? From your code i see you run at prio 98. What about the IRQ handlers? And the softirq's, too? Other software?
Flo
P.S.: I ran the test a few [20 or so] times and didn't get any failures of the sort you see. Even with a 1ms period:
~/downloads$ ./sched_latency_lkml ------------------------------- Scheduling Latency -------------------------------
Running 10000 iterations with a period of 1 ms Expected running time: 10 s
ITERATION DELAY(US) MAX_DELAY(US) FAILURES --------- --------- ------------- -------- 10000 32 47 0
Start Latency: 305 us: FAIL Min Latency: 16 us: PASS Avg Latency: 29 us: PASS Max Latency: 47 us: PASS Failed Iterations: 0
~/downloads$ uname -a Linux mango.fruits 2.6.16-rt20 #4 PREEMPT Wed May 10 12:53:39 CEST 2006 i686 GNU/Linux
Ooops, i must admit i have the nvidia binary only kernel module loaded, but i suppose this wouldn't make a difference for the better ;)
I got high resolution timers enabled and left the softirq threads at their defaults.
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