linux-kernel - Re: A question of perf NMI handler

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Message-ID: <20100806142131.GA1874@redhat.com>
Date:	Fri, 6 Aug 2010 10:21:31 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Robert Richter <robert.richter@....com>
Cc:	Cyrill Gorcunov <gorcunov@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Lin Ming <ming.m.lin@...el.com>, Ingo Molnar <mingo@...e.hu>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Huang, Ying" <ying.huang@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: A question of perf NMI handler

On Fri, Aug 06, 2010 at 08:52:03AM +0200, Robert Richter wrote:
> On 04.08.10 15:26:34, Cyrill Gorcunov wrote:
> 
> > yes, that is what I meant by nmi_sc register. I think we need to restucturize
> > current default_do_nmi handler but how to be with perfs I don't know at moment
> > if perf register gets overflowed (ie already has pedning nmi) but we handle
> > it in early nmi cycle this would lead to strange results. Need to think.
> > 
> > > 
> > > So you can decide to either get an unrecovered nmi panic triggered by
> > > a perfctr or losing unknown nmis from other sources. Maybe this can be
> > > fixed by implementing handlers for those sources.
> 
> I was playing around with it yesterday trying to fix this. My idea is
> to skip an unkown nmi if the privious nmi was a *handled* perfctr

You might want to add a little more logic that says *handled* _and_ had
more than one perfctr trigger.  Most of the time only one perfctr is
probably triggering, so you might be eating unknown_nmi's needlessly.

Just a thought.

> nmi. I will probably post an rfc patch early next week.
> 
> Another problem I encountered is that unknown nmis from the chipset
> are not reenabled, thus when hitting the nmi button I only see one
> unknown nmi message per boot, if I reenable it, I get an nmi
> storm firing nmi_watchdog. Uhh....

Interesting.

Cheers,
Don
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