Re: liveloock using PREEMPT_RT with i915 driver

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2025-06-18 07:34:25 [-0400], Michael Schanne wrote:
> I found my issue, I am using several SCHED_FIFO threads, one was spinning
> waiting on a timer to update, another thread which was supposed to update
> the timer count is higher priority, but with the RT patch applied there is
> also a ktimers thread set to RT priority 1, so it was never getting a
> chance to run and my timer would never fire.  I adjusted the ktimers thread
> to a higher priority and things started working again.  This thread does
> not exist in the vanilla kernel even with CONFIG_PREEMPT_RT enabled, so
> that is why I wasn't seeing it there.  The i915 driver was a red herring.

Okay not the i915.
The ktimers thread wakes only SCHED_OTHER tasks. The SCHED_FIFO/RR
threads should be woken up directly (without the need of the ktimers
thread).
So you are not using clock_nanosleep() but something like a POSIX timer?

> Thanks,
> Mike

Sebastian