linux-kernel - Re: introduce NMI_AUTO as nmi

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Message-ID: <20100113093240.GC6739@elte.hu>
Date:	Wed, 13 Jan 2010 10:32:40 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Don Zickus <dzickus@...hat.com>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>, aris@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: introduce NMI_AUTO as nmi_watchdog option


* Don Zickus <dzickus@...hat.com> wrote:

> On Mon, Jan 11, 2010 at 11:27:29PM +0300, Cyrill Gorcunov wrote:
> > On Mon, Jan 11, 2010 at 02:16:33PM -0500, Don Zickus wrote:
> > > Hi Ingo,
> > > 
> > ...
> > > I was going to jump in and try to do this work.  I wanted to make sure
> > > what you were looking for here.  When you say convert nmi watchdog to perf
> > > events, I assume you mean merging over the bits of perfctr-watchdog.c to
> > > perf_events.c, modify nmi.c to just register as a normal perf event and
> > > probably cleanup the oprofile stuff to match, correct?
> > > 
> > > Cheers,
> > > Don
> > >
> > 
> > As far as I know -- converting perfctr-watchdog.c to into perfevents
> > style would be quite a desirable feature. But I still didn't manage to
> > find time for this task :( If you're interested to start this work
> > -- that would be just great!
> 
> 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.

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

	Ingo
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