Re: 4.14-rt timer issues using PREEMPT_RT_FULL=y and NO_HZ_FULL_ALL=y

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

On 2017-12-14 19:01:50 [+0100], bert schulze wrote:
> > It looks that if you set rcu_normal_after_boot to 0 in
> > kernel/rcu/update.c then other problem should go away and everything is
> > "normal" now, right?
> 
> System boots reliable with mentioned patch applied, and nanosleep is
> working as well! I do not have to set rcu_normal_after_boot to 0 or what
> is its purpose?

By default RT sets rcu_normal_after_boot to 1. And with it set to 1 the
system seems to freeze somehow. After switching it back to 0 the system
works more reliably.

> > Now I need to figure why that is broken…
> 
> Guess you already did :)
no, not yet.

> root@deb9:~# bash test 
> # uname -a
> Linux deb9.virt 4.14.3-rt5-rt+ #5 SMP PREEMPT RT Thu Dec 14 18:39:27 CET 2017 x86_64 GNU/Linux
> # cat /proc/sys/kernel/timer_migration
> 1
> # dmesg | grep hrtimer
> # date
> Thu Dec 14 18:41:21 CET 2017
> # grep LOC /proc/interrupts
> LOC:       8002        208        138         68   Local timer interrupts
> # for cpu in {0..3} ;do time taskset -ac  sleep 0.1 ;done
> real    0m0.103s
> real    0m0.105s
> real    0m0.105s
> real    0m0.105s
> # date
> Thu Dec 14 18:41:22 CET 2017
> # grep LOC /proc/interrupts
> LOC:       8437        209        139         70   Local timer interrupts
> 
> Tested on bare hardware and QEMU, top and cyclictest are working as well
> no more interrupt storms can be observed!

hmm. So just that patch and everything works for you? No hangups during
boot, no "perf: interrupt took too long" every 30-60 secs?

> > 
> Thank you!
> Bert

Sebastian