Messages in this thread | | | Subject | Re: [V2 PATCH 0/6] x86, NMI: give NMI handler a face-lift | From | Peter Zijlstra <> | Date | Thu, 18 Nov 2010 21:30:33 +0100 |
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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).
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