Re: SCHED_RR and kernel threads

[Con Kolivas <kernel@kolivas.org>]

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Stephen Warren wrote:
> Hello.
> 
> We have an application that is running on kernel 2.6.9. This application
> makes use of real-time threads, namely using the SCHED_RR policy.
> 
> It appears that during times of high application CPU usage, some
> *kernel* threads don't get to run. As an example, this means that local
> keyboard presses aren't processed (or are processed very slowly) by the
> kernel, so our application never sees them. This has the effect of
> hanging the system, since the way to get out of the higher CPU usage
> portion of the application is to press the ESC key, and our application
> never sees that keypress.
> 
> 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.

Cheers,
Con

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