Re: [PATCH v3 3/3] softirq: Use a dedicated thread for timer wakeups on PREEMPT_RT.

[Sebastian Andrzej Siewior]

On 2025-12-02 07:57:04 [+0100], Jan Kiszka wrote:
> So, we have this right now in the 6.12-rt and 6.1-rt trees. The patch
> (b12e35832805) that enabled the lockup above was added to 4.18. In
> 4.19-rt (still under maintenance via 4.19-cip-rt), we had ktimersoftd -
> was that addressing the issue as well? Or could timers have expired back
> then also outside of that thread, thus potentially without SCHED_FIFO prio?

Looking at v4.19.25-rt16, there is ktimersoftd/ via "softirq: split
timer softirqs out of ksoftirqd". This became later ktimers/.
So yes, the timer should be expired with a SCHED_FIFO priority.

You are most likely aware of "Defer throttle when task exits to user"
	https://lore.kernel.org/all/20250829081120.806-1-ziqianlu@xxxxxxxxxxxxx/

> Thanks,
> Jan

Sebastian