linux-kernel - Re: introduce NMI_AUTO as nmi

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Date:	Wed, 13 Jan 2010 11:23:03 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>, aris@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: introduce NMI_AUTO as nmi_watchdog option

On Wed, Jan 13, 2010 at 10:32:40AM +0100, Ingo Molnar wrote:
> > After looking through the code I just had some questions, perhaps you have 
> > thought about this longer than me, what to do with the reservation code 
> > (just remove it I assume and let perf_events _be_ the only code that
> >  handles perf events) and what to do with some of the cpu quirks as noted in 
> > perfctr-watchdog.c (notable some of the Intel errata for the Core chipsets).
> 
> Given the amount of quirks in the perctr code it might make sense to shape 
> this as a new feature initially: introduce a new NMI watchdog that is perf 
> based and has a different codebase.
> 
> Then, once it's capable enough and has been in circulation long enough we can 
> simply drop the old NMI watchdog. (without users noticing anything [modulo 
> bugs])
> 
> v1 should concentrate on x86 CPUs that are supported by perf currently. Note, 
> it _might_ make sense to do it via a new kernel/nmi_watchdog.c file - other 
> architectures have NMI concepts as well, such as Sparc64. A further idea would 
> be to maybe even merge it with the softlockup code in kernel/softlockup.c - so 
> that we dont have two sets of apis like touch_nmi_watchdog and 
> touch_softlockup_watchdog.

Ok, interesting.  Right now I am working on making sure I know how to
register something with the perf event framework (from kernel space).
Once I can do that, I'll expand it outward and see where it goes. :-)

> 
> So there's a wide spectrum of possibilities - the important thing is to start 
> small :-)

I see. Thanks.

Cheers,
Don
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