Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift

From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Don Zickus <dzickus@redhat.com>
Cc: Jason Wessel <jason.wessel@windriver.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@elte.hu>,
	Robert Richter <robert.richter@amd.com>,
	ying.huang@intel.com, Andi Kleen <andi@firstfloor.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift
Date: Thu, 18 Nov 2010 23:11:18 +0300	[thread overview]
Message-ID: <20101118201118.GC6028@lenovo> (raw)
In-Reply-To: <20101118200807.GC8131@redhat.com>

On Thu, Nov 18, 2010 at 03:08:07PM -0500, Don Zickus wrote:
> On Thu, Nov 18, 2010 at 01:51:44PM -0600, Jason Wessel wrote:
> > > So the problem is when the nmi watchdog is enabled, the perf event is
> > > 'active' and thus tries to read the counter value.  Because it is always
> > > zero, perf just assumes the counter overflowed and the NMI is his.
> > >
> > > Not sure how to fix it yet, other than include the logic that detects we
> > > are on a guest and disable perf??
> > >
> > >   
> > 
> > I highly doubt we want to disable perf.   I would rather use the source
> > and fix the nmi emulation in KVM/Qemu after we hear back the results
> 
> Well I think Peter does not have a positive opinion about emulating perf
> inside a guest.  Nor are the KVM folks having much success in doing so.
> 
> Just to clarify, perf counter emulation is _not_ implemented in kvm.
> Therefore disabling perf in the guest makes sense until someone gets
> around to actually writing the emulation code for perf in a guest. :-)
> 
> Cheers,
> Don

ok, Don, but you mentioned there are false alarms on real P4 machine, right?

 Cyrill