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Message-ID: <1331828203.18960.200.camel@twins>
Subject: Re: [PATCH] watchdog: Make sure the watchdog thread gets CPU on
 loaded system
From: Peter Zijlstra <peterz@infradead.org>
To: Mandeep Singh Baines <msb@chromium.org>
Cc: Don Zickus <dzickus@redhat.com>, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
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Date: Thu, 15 Mar 2012 17:16:43 +0100
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On Thu, 2012-03-15 at 17:11 +0100, Peter Zijlstra wrote:
> On Thu, 2012-03-15 at 17:10 +0100, Peter Zijlstra wrote:
> > On Thu, 2012-03-15 at 08:39 -0700, Mandeep Singh Baines wrote:
> > > Its a good tool for catching problems of scale. As we move to more and
> > > more cores you'll uncover bugs where data structures start to blow up.
> > > Hash tables get huge, when you have 100000s of processes or millions
> > > of
> > > TCP flows, or cgroups or namespace. That critical section (spinlock,
> > > spinlock_bh, or preempt_disable) that used to be OK might no longer
> > > be.
> > 
> > Or you run with the preempt latency tracer.
> 
> Or for that matter run cyclictest...

Thing is, if you want a latency detector, call it that and stop
pretending its a useful debug feature. Also, if you want that, set the
interval in the 0.1-0.5 seconds range and dump stack on every new max.