linux-kernel - Re: [PATCH] ftrace based hard lockup detector

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Message-ID: <alpine.DEB.1.10.0901190757330.17050@gandalf.stny.rr.com>
Date:	Mon, 19 Jan 2009 07:59:01 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ftrace based hard lockup detector



On Sun, 18 Jan 2009, Frederic Weisbecker wrote:

> Like the NMI watchdog, this feature try to detect hard lockups by
> lurking at the non-progress of the timer interrupts.
> 
> You can enable it at boot time by passing the ftrace_hardlockup parameter.
> I plan to add a debugfs file to enable/disable at runtime.
> 
> When a hardlockup is detected, it will print a backtrace. Perhaps it
> would be good to print the locks held from lockdep too?
> 
> It only support x86 for the moment, because a kind of generic timer interrupt
> counter is needed on all archs to have it generic.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>

Hi Frederic,

This seems like a rewrite of the NMI lockup code. In my debugging, I 
simply put ftrace_dump in the NMI lockup, which gives me a ftrace dump as 
soon as NMI detects a lockup. I'm a bit confused at what this gives us 
over that?

-- Steve
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