Re: [PATCH] sched - Implement priority and fifo support for SCHED_ISO

[Con Kolivas <kernel@kolivas.org>]

Jack O'Quin wrote:
> The fact that the results did improve with the 90% setting suggests
> that there may be a bug in your throttling or time accounting.  The
> DSP load for this test should hover around 50% when things are working
> properly.  It should never hit a 70% limit, not even momentarily.  The
> background compile should not affect that, either.
> 
> Something seems to be causing scheduling delays when the sound card
> interrupt causes jackd to become runnable.  Ingo's nice(-20) patches
> seem to have the same problem, but his RLIMIT_RT_CPU version does not.

Good work. Looks like you're probably right about the accounting. It may 
be as simple as the fact that it is on the timer tick that we're getting 
rescheduled and this ends up being accounted as more since the 
accounting happens only at the scheduler tick. A test run setting 
iso_cpu at 100% should tell you if it's accounting related - however the 
RLIMIT_RT_CPU patch is accounted in a similar way so I'm not sure there 
isn't another bug hanging around. I'm afraid on my hardware it has been 
behaving just like SCHED_FIFO for some time which is why I've been 
hanging on your results. You're not obliged to do anything (obviously), 
but the 100% run should help discriminate where the problem is.

Since I've come this far with the code I'll have another look for any 
other obvious bugs.

Cheers,
Con