Re: 6.1-rt: NOHZ tick-stop error: local softirq work is pending

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

On 2025-02-25 16:16:25 [+0100], Florian Bezdeka wrote:
> > which version is this? I think is is an imported issue. Is v6.1.119-rt45
> > also affected?
> 
> This is a typo, right? You mean it is an important issue, no?

No, the version is correct. And I meant "imported" as in we got it from
the stable queue.

> We can see that on
> 
> - v6.1.90-rt (Debian -rt kernel)
> - v6.1.120-rt (Debian -rt kernel)
> - v6.1.119-rt45 (So yes, this is also affected)
> - v6.1.120-rt47

But if this is visible on v6.1.90-rt then it is not originating from
what I assumed.

> With PERIODIC you mean CONFIG_HZ_PERIODIC, right?
correct.

> We have CONFIG_NO_HZ_FULL=y set but do net set the nohz_full= cmdline
> parameter, so that we should get CONFIG_NO_HZ_IDLE behavior at the end.
> 
> I realized today that the warning is somehow related to our RT tuning.
> Enabling NAPI threading makes the warning go away, even if NAPI threads
> are tuned the same way as ksoftirqd.
NAPI threads? You have RPS enabled by any chance?
Would commit
    dad6b97702639 ("net: Allow to use SMP threads for backlog NAPI.")
    80d2eefcb4c84 ("net: Use backlog-NAPI to clean up the defer_list.")

help?

> I will have to look into that in more depth.
> 
> Thanks for your input Sebastian.

You are welcome.

Sebastian