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Message-ID: <20161118183633.GA25157@e106950-lin.cambridge.arm.com>
Date: Fri, 18 Nov 2016 20:23:38 +0000
From: Brian Starkey <brian.starkey@....com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Eric Dumazet <edumazet@...gle.com>,
LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexander Potapenko <glider@...gle.com>,
Steven Rostedt <rostedt@...dmis.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: Regression: Failed boots bisected to 4cd13c21b207 "softirq: Let
ksoftirqd do its job"
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
>
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