Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let ksoftirqd do its job"

[Brian Starkey]

Hi Thomas,

On Fri, Nov 18, 2016 at 01:40:43AM +0100, Thomas Gleixner wrote:
> Brian,
>
> On Thu, 17 Nov 2016, Brian Starkey wrote:
> > No joy with this patch :-(
> >
> > I had to add an ioaddr argument because apparently that macro depends
> > on local context (yuck...), but it doesn't help my issue.
> >
> > FWIW I don't see any timeouts, either with or without the patch.
> > (I don't know for sure, but I would guess that the model of the
> > network card doesn't model whatever stall that loop is checking for.
> > It probably just completes all MMU operations immediately)
>
> Is there a chance that you enable trace points at the kernel command line?
>
>  trace_event=sched_wakeup,sched_switch,irq_handler_entry,irq_handler_exit,softirq_raise,softirq_entry,softirq_exit
>
> should be enough for a start. All we need aside of that is a trigger to
> stop the trace so we can actually see the events around the time where
> things go stale.
>
> I assume that the whole issue is visible throughout the slow progress of
> init towards a working system, so for a start it would be sufficient to add
> something like this into the startup sequence at some point:
>
> mount -t debugfs debugfs /sys/kernel/debug
> echo 0 >/sys/kernel/debug/tracing/tracing_on
>
> The only interesting challange is to get the trace data out of the
> system. The trace is accessible via:
>
> cat /sys/kernel/tracing/trace

Thanks for the pointers on tracing. I haven't used it before so that
was very helpful.

> So if your ssh works at some point, that might be an option or you just try
> to store it over NFS (which will be slow, but better than nothing). Maybe
> you have a better idea :)

I've tried a whole bunch of different ways to reproduce the problem
and get the logs out, so far they've all been unsuccessful
(reproducing is easy, getting data out is not).

I have a few more ideas to try, but it's pretty slow work - it's
taking at least 30 minutes per attempt. I'll let you know if I manage
something.

Thanks!
-Brian

> Thanks,
>
> 	tglx