linux-kernel - Re: [PATCH 3/3 v2] nmi_watchdog: config option to enable new nmi

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Date:	Mon, 8 Feb 2010 12:39:06 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Don Zickus <dzickus@...hat.com>, peterz@...radead.org,
	aris@...hat.com, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 3/3 v2] nmi_watchdog: config option to enable new 
	nmi_watchdog

On 2/8/10, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Don Zickus <dzickus@...hat.com> wrote:
>
>> +config NMI_WATCHDOG
>> +	bool "Detect Hard Lockups with an NMI Watchdog"
>> +	depends on DEBUG_KERNEL && PERF_EVENTS
>> +	default y
>> +	help
>> +	  Say Y here to enable the kernel to use the NMI as a watchdog
>> +	  to detect hard lockups.  This is useful when a cpu hangs for no
>> +	  reason but can still respond to NMIs.  A backtrace is displayed
>> +	  for reviewing and reporting.
>> +
>> +	  The overhead should be minimal, just an extra NMI every few
>> +	  seconds.
>
> Thought for later patches: I think an architecture should be able to express
> via a Kconfig switch that it actually _has_ NMI events. There's
> architectures
> which dont have a PMU driver and only have software events. There's also
> architectures that have a PMU driver but no NMIs.
>
> Something like ARCH_HAS_NMI_PERF_EVENTS?
>
> Also, i havent checked, but what is the practical effect of the new generic
> watchdog on x86 CPUs that does not have a native PMU driver yet - such as
> P4s?
>

p4 pmu is not yet implemented. I'll try to post on lkml the thnigs
i've done for it today evening, though it's pretty ugly i would say.

> Anyway, i'll create a tip:perf/nmi topic branch for these patches, it
> certainly looks like a useful generalization and a new architecture that has
> perf could easily enable it, without having to write its own NMI watchdog
> implementation. It's also useful for any new watchdog features that people
> might want to add. Plus it makes the x86 PMU code cleaner in the long run as
> well.
>
> Thanks,
>
> 	Ingo
>
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