> -----Original Message-----
> From: Jan Kiszka <jan.kis...@siemens.com>
> Sent: Montag, 17. Februar 2020 18:16
> To: Lange Norbert <norbert.la...@andritz.com>; Xenomai
> (xenomai@xenomai.org) <xenomai@xenomai.org>
> Subject: Re: Still some lockups when enabling ftrace
>
> NON-ANDRITZ SOURCE: BE CAUTIOUS WITH CONTENT, LINKS OR
> ATTACHMENTS.
>
>
> On 17.02.20 17:57, Jan Kiszka via Xenomai wrote:
> > On 17.02.20 17:50, Lange Norbert via Xenomai wrote:
> >> I managed to narrow it down to this:
> >>
> >> trace-cmd start -e 'tlb:tlb_flush'
> >>
> >> Seems to bug the kernel even if no cobalt thread is running, only a
> >> rt_igb and the rtnet stack.
> >>
> >
> > OK, that was already my idea as well.
> >
> > That rcu_irq_enter_irqson must not be there. Trying to understand
> > right now how it can sneak in. What are your RCU configs?
> >
>
> Found it.
>
> Preconditions: CONFIG_PREEMPT_NONE/VOLUNTARY ->
> CONFIG_TREE_RCU
>
> Now switch_mm_irqs_off, which we also use for primary tasks, carries some
> trace_tlb_flush_rcuidle. The "_rcuidle" appendix makes the difference. Such
> tracepoints end up in tracepoint.h's __DO_TRACE in the rcuidle path that
> contains a rcu_irq_enter_irqson of this form:
>
> void rcu_irq_exit_irqson(void)
> {
> unsigned long flags;
>
> local_irq_save(flags);
> rcu_irq_exit();
> local_irq_restore(flags);
> }
>
> And those local_irq* bite us. With CONFIG_TINY_RCU, rcu_irq_exit_irqson is
> empty.
>
> I guess we need to skip the problematic tracepoints, either when I-pipe is on
> or when the caller is in the primary domain.
That rcuidle sprung into my eye aswell, but not because I have any clue what
happens
in the system.
I asked some time ago, about related stuff (IPI,
MEMBARRIER_CMD_PRIVATE_EXPEDITED)
Related to Lttng whether those are safe to use at all.
IPIs still are interrupts and will have to affect Cobalt AFAIK, and a lot of
assertions are
That they are very fast (while they might be blocked a couple ms with realtime
tasks).
https://www.xenomai.org/pipermail/xenomai/2019-November/042080.html
Quite good you found it that fast anyway ;)
Thanks, Norbert
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