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SubjectRE: SCHED_RR and kernel threads
> From: Con Kolivas [] 
> Stephen Warren wrote:
> > It appears that during times of high application CPU usage, some
> > *kernel* threads don't get to run.
> > ...
> > This appears to be due to the fact that the kernel threads are all
> > SCHED_OTHER, so our SCHED_RR user-space application trumps them!
> Don't run your userspace at SCHED_RR? The kernel threads are
> SCHED_NORMAL precisely for the reason that you wont get real time
> performance if the kernel threads rear their ugly heads,
> albeit rarely.

We have actually set the kernel threads to priority SCHED_RR 50, and
most user-space threads to SCHED_RR priority 50. Some critical
user-space threads are above priority 50.

Won't this allow the kernel and user space threads to co-operate nicely
all the time?

What is it specifically that will make kernel SCHED_RR threads cause
non-real-time operation? If it's just a bunch of corner cases or odd
conditions, we may be in an environment we can control so that doesn't

I guess we could have most threads stay at SCHED_NORMAL, and just make
the few critical threads SCHED_RR, but I'm getting a lot of push-back on
this, since it makes our thread API a lot more complex.

Stephen Warren, Software Engineer, NVIDIA, Fort Collins, CO
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