Re: How to investigate different timings of 2 HW with same kernel ?

[Daniel Wagner <wagi@xxxxxxxxx>]

Hi Ran,

> Testing is done using:
> https://github.com/nma/preempt-rt/blob/master/test-rt.c

I just noticed this:

#define MY_PRIORITY (49) /* we use 49 as the PRREMPT_RT use 50
                            as the priority of kernel tasklets
                            and interrupt handler by default */

...
        param.sched_priority = MY_PRIORITY;
        if(sched_setscheduler(0, SCHED_FIFO, &param) == -1) {
                perror("sched_setscheduler failed");
                exit(-1);
        }
...

The man page on sched_setscheduler:

       SCHED_FIFO    a first-in, first-out policy; and
       SCHED_RR      a round-robin policy.

       For each of the above policies, param->sched_priority specifies
       a scheduling priority for the thread.  This is a number in the
       range  returned  by calling  sched_get_priority_min(2)  and
       sched_get_priority_max(2) with the specified policy.  On Linux,
       these system calls return, respectively, 1 and 99.

Thus you should pick a priority higher then the default IRQ thread
priorities, e.g. 51 should do the trick.

Thanks,
Daniel
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