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Date: Thu, 18 Feb 2016 20:13:18 -0800
Message-ID: <CALAqxLXrGB8yiP469yGBHTBbX3+4p-qC0QNPoqq+q_ju0Nq+vQ@mail.gmail.com>
Subject: Re: rcu_preempt self-detected stall on CPU from 4.5-rc3, since 3.17
From: John Stultz <john.stultz@linaro.org>
To: Ross Green <rgkernel@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        lkml <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Lai Jiangshan <jiangshanlai@gmail.com>, dipankar@in.ibm.com,
        Andrew Morton <akpm@linux-foundation.org>,
        Josh Triplett <josh@joshtriplett.org>, rostedt <rostedt@goodmis.org>,
        David Howells <dhowells@redhat.com>,
        Eric Dumazet <edumazet@google.com>,
        Darren Hart <dvhart@linux.intel.com>,
        =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= <fweisbec@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, pranith kumar <bobby.prani@gmail.com>
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On Thu, Feb 18, 2016 at 7:56 PM, Ross Green <rgkernel@gmail.com> wrote:
> Well a bonus extra!
> Kept everything running and there was another stall.
> So i have included the demsg output for perusal.
>
> Just to clear things up there is no hotplug involved in this system.
> It is a standard Pandaboard ES Ti4460 two processor system.
> I use this for testing as a generic armv7 processor, plus can keep it
> just running along for testing for a long time. the system has a total
> of 23-25 process running on average. Mainly standard daemons. There is
> certainly no heavy processing going on. I run a series of benchmarks
> that are cpu intensive for the first 20 miinutes after boot and then
> just leave it idle away. checking every so often to see how it has
> gone.
> As mentioned I have observed these stalls going back to 3.17 kernel.
> It will often take up to a week to record such a stall. I will
> typically test every new release kernel, so the -rc? series will get
> around a weeks testing.

Sorry. Kind of hopping in a bit late here. Is this always happening
with just the pandaboard? Or are you seeing this on different
machines?

Have you tried enabling CONFIG_DEBUG_TIMEKEEPING just in case
something is going awry there?

thanks
-john