Re: rt20 scheduling latency testcase and failure data

On Fri, 12 May 2006 19:24:53 -0700
Darren Hart <dvhltc@xxxxxxxxxx> 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.

--
Palimm Palimm!
http://tapas.affenbande.org
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