Re: rt20 scheduling latency testcase and failure data

[Darren Hart <dvhltc@us.ibm.com>]

On Monday 15 May 2006 04:20, Sébastien Dugué wrote:
> On Sat, 2006-05-13 at 11:06 -0700, Darren Hart wrote:
> > These tests are running on a 4 way opteron at 2 GHz with 4 GB RAM.  I
> > have attached the .config and a listing of all the rt tasks running on
> > the system (which addresses the questions regarding priority setup, IRQ
> > handlers, and softirqs - all default).  I am running with the futex
> > priority based wakeup patches from Sebastien Duque, but I don't think
> > this test excercises those paths.
>
>   Which watchdog are you using here? Have you tried without the
> watchdog?

Those are the softlockup watchdog threads (kernel/softlockup.c).  They run 
once a second and reports a bug if the watchdog failed to run in 10 seconds.  
It is difficult to reproduce but at run 126 (1,260,000 iterations) it finally 
failed.  Note that I am only counting runs that completely miss an entire 
period as a failure for the purposes of this test.  I want to knock out the 
10+ms latencies before I concern myself too much with the >100us failures :-)

--------------------
ITERATION 26
--------------------
-------------------------------
Scheduling Latency
-------------------------------

Running 10000 iterations with a period of 5 ms
Expected running time: 50 s

ITERATION DELAY(US) MAX_DELAY(US) FAILURES
--------- --------- ------------- --------


PERIOD MISSED!
     scheduled delta:     4076 us
        actual delta:    14892 us
             latency:    10815 us
---------------------------------------
      previous start: 18365818 us
                 now: 18366739 us
     scheduled start: 18360000 us
next scheduled start is in the past!


Start Latency:  106 us: FAIL
Min Latency:      8 us: PASS
Avg Latency:      4 us: PASS
Max Latency:   10818 us: FAIL
Failed Iterations: 1


It's interesting, this 10ms latency seems to be the most common result.  I'm 
going to take a look at ingo's tracing script now, more info a bit later...

-- 
Darren Hart
IBM Linux Technology Center
Realtime Linux Team