Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760223Ab0KRUab (ORCPT ); Thu, 18 Nov 2010 15:30:31 -0500 Received: from canuck.infradead.org ([134.117.69.58]:49252 "EHLO canuck.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756773Ab0KRUaa convert rfc822-to-8bit (ORCPT ); Thu, 18 Nov 2010 15:30:30 -0500 Subject: Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift From: Peter Zijlstra To: Don Zickus Cc: Jason Wessel , Ingo Molnar , Robert Richter , ying.huang@intel.com, Andi Kleen , LKML , Frederic Weisbecker In-Reply-To: <20101118200807.GC8131@redhat.com> References: <20101112161144.GP4823@redhat.com> <4CDD6CAD.30303@windriver.com> <20101112172755.GR4823@redhat.com> <20101116184325.GB4823@redhat.com> <4CE2E3C3.6060800@windriver.com> <20101118080516.GJ32621@elte.hu> <4CE52048.5080802@windriver.com> <1290086232.2109.1507.camel@laptop> <20101118193247.GF18100@redhat.com> <4CE583D0.8050407@windriver.com> <20101118200807.GC8131@redhat.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Thu, 18 Nov 2010 21:30:33 +0100 Message-ID: <1290112234.2109.1534.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1778 Lines: 43 On Thu, 2010-11-18 at 15:08 -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. Well, I'll let someone else write it.. I tihnk its pretty pointless to have, the whole virt layer totally destroys many (if not all) useful metrics. But I don't have a problem with full msr emulation, what I do not like is a direct msr passthough bypassing perf. > Nor are the KVM folks having much success in doing so. Just busy doing other stuff I guess.. Jes was going to prod at it at some point. > 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. :-) Right, which is what I proposed, on init do a checking_wrmsrl() on a known PMU reg, KVM/qemu should fault on that.. (I'd prefer it if they'd also fault on reading it too). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/