[LITMUS^RT] Missing st_trace records

[Björn Brandenburg]

On 06 Nov 2014, at 18:00, Mikyung Kang <mkkang01 at gmail.com> wrote:

> Even though I tried several $PROG, inter-run variation happened.
> I pasted the result of 90% utilzation and 45% utilization cases below. 
> I used different (period,wcet) per task at this time.
> 
> (1) 8 * 0.9 utilization/core ==> (4, 8, 5, 3, 2, 4, 8, 4, 1, 7) tasks are schedulable among 8 tasks. ==> schedulability (0.50, 1.00, 0.63, 0.38, 0.25, 0.50, 1.00, 0.50, 0.13, 0.88)

How can a subset of a tasks be schedulable under G-EDF? As far as I know, no schedulability analysis has been published to date that would allow you to arrive at such a conclusion.

Please, let's use a consistent terminology: NOT observing any deadline misses does NOT imply that a task set (or a task) is schedulable. The absence of observed faults cannot prove the correctness of a system.

> (2) 5 * 0.9 utilization/core ==> (4, 5, 5, 5, 4, 5, 4, 5, 5, 5) tasks are schedulable among 5 tasks.
> (3) 8 * 0.45 utilization/core ==> (4, 3, 7, 6, 4, 6, 4, 7, 6, 4) tasks are schedulable among 8 tasks.
> (4) 5 * 0.45 utilization/core ==> (5, 2, 3, 4, 2, 3, 5, 4, 4, 3) tasks are schedulable among 5 tasks.

I don't understand these calculations. How do you know the workload that you are launching is even feasible? In other words, why are you even surprised to see deadline misses?

> That is, in case of 1st run of (1), 4 tasks have correct (period, cost) and the other 4 tasks have (period=0, cost=0).
> 
> # Task,   Job,     Period,   Response, DL Miss?,   Lateness,  Tardiness
> # task NAME=rt_launch PID=43217 COST=139000000 PERIOD=155000000 CPU=0
>  43217,     2,  155000000,  139123829,        0,  -15876171,          0
>  43217,     3,  155000000,  139120144,        0,  -15879856,          0
>  43217,     4,  155000000,  139121134,        0,  -15878866,          0
>  43217,     5,  155000000,  139113222,        0,  -15886778,          0
> ...
> 
> # task NAME=<unknown> PID=43215 COST=0 PERIOD=0 CPU=-1
>  43215,     2,          0,  159116315,        0,  -17883685,          0
>  43215,     3,          0,  159133056,        0,  -17866944,          0
>  43215,     4,          0,  159121530,        0,  -17878470,          0
>  43215,     5,          0,  159130841,        0,  -17869159,          0
>  43215,     6,          0,  159142111,        0,  -17857889,          0
> 
> Any hint/comments are welcome! I'll appreciate it!

Glenn pointed this out already. If cost/period are equal to zero, then the ST_PARAM record is missing from the trace. You can easily verify this yourself by inspecting the st_job_stats source code. Missing records at the beginning of the trace most likely indicate that you are starting to trace only after the task has already been set up. 

- Björn