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Date: Wed, 2 Sep 2015 08:50:28 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Shaohua Li <shli@fb.com>, Thomas Gleixner <tglx@linutronix.de>,
        John Stultz <john.stultz@linaro.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Prarit Bhargava <prarit@redhat.com>,
        Richard Cochran <richardcochran@gmail.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Ingo Molnar <mingo@kernel.org>, Clark Williams <williams@redhat.com>
Subject: Re: [PATCH 8/9] clocksource: Improve unstable clocksource detection
Message-ID: <20150902065028.GP16853@twins.programming.kicks-ass.net>
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On Tue, Sep 01, 2015 at 03:35:18PM -0400, Steven Rostedt wrote:
> On Tue, 1 Sep 2015 11:14:17 -0700
> Shaohua Li <shli@fb.com> wrote:
> 
> > > You think that blocking softirq execution for 42.9 seconds is normal?
> > > Seems we are living in a different universe.
> > 
> > I don't say it's normal. I say it's not hard to trigger.
> > 
> > > > it's just VM off. A softirq can hog the cpu.
> > > 
> 
> Please provide a test case that shows the softirq hogging the cpu for
> over 40 seconds.

Do not overlook the MAX_SOFTIRQ_* logic while you're there trying to
explain this ;-)

A softirq running significantly longer than 2 jiffies and not falling
back to ksoftirq is a plain bug.