[LITMUS^RT] high miss ratio for low task utilization

[Björn Brandenburg]

> On 21.11.2014, at 16:41, jp walters <mailinglistjp39 at gmail.com> wrote:
> 
> Which traces are you interested in?  I can recreate the 3-task system easily enough, and I can capture /dev/litmus/log.  I can also use feather trace to get /dev/litmus/sched_traceX data. 

Until we suspect a real bug in the kernel I'm mainly interested in sched_trace data. 

> Poking around the list, I've seen recommendations to use the following to parse out the sched_trace logs:
> 
> https://github.com/brandenburg/sched-trace-tools
> 
> I pulled that down, and using the job_stats tool on the output from st_trace, I'm left with plaintext data that looks like below (one for each CPU).  I'm probably doing something wrong though.
> 
> root at ubuntu-qemu:~/non-script.data# cat simple0

Make sure you give the tool all
per-CPU files together to analyze the complete trace. The data below looks like per-CPU data (huge gaps in the job sequence numbers).

> # Task,   Job,     Period,   Response, DL Miss?,   Lateness,  Tardiness
> # task NAME=<unknown> PID=3802 COST=0 PERIOD=0 CPU=-1
>   3802,     9,          0,   30657540,        0,  -29342460,          0
>   3802,    13,          0,   32616504,        0,  -27383496,          0
>   3802,    39,          0,   30793032,        0,  -29206968,          0
>   3802,    89,          0,   29259038,        0,  -30740962,          0
>   3802,    93,          0,   29860287,        0,  -30139713,          0
>   3802,    97,          0,   29485435,        0,  -30514565,          0
>   3802,   101,          0,   30333923,        0,  -29666077,          0
>   3802,   131,          0,   30122722,        0,  -29877278,          0
>   3802,   135,          0,   30649661,        0,  -29350339,          0
> # task NAME=<unknown> PID=3801 COST=0 PERIOD=0 CPU=-1

This looks totally ok. All jobs in this trace have zero tardiness / negative lateness and met their deadlines. I don't see a problem here. 

- Björn 
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