Re: question on sched-rt group allocation cap: sched_rt_runtime_us

From: Lucas De Marchi
Date: Sat Sep 05 2009 - 18:42:29 EST

> You say you pin the threads to a single core: how many cores does your
> system have?
> If this is the case, this behavior is the expected one, the scheduler
> tries to reduce the number of migrations, concentrating the bandwidth
> of rt tasks on a single core.  With your workload it doesn't work well
> because runtime migration has freed the other core(s) from rt bandwidth,
> so these cores are available to SCHED_OTHER ones, but your SCHED_OTHER
> thread is pinned and cannot make use of them.

Indeed. I've tested this same test program in a single core machine and it
produces the expected behavior:

rt_runtime_us / rt_period_us % loops executed in SCHED_OTHER
95% 4.48%
60% 54.84%
50% 86.03%
40% OTHER completed first

Lucas De Marchi
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