Messages in this thread | | | Date | Tue, 13 Dec 2011 15:51:26 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [patch 0/3] kvm tool: Serial emulation overhaul |
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On Tue, 13 Dec 2011, Avi Kivity wrote: > On 12/13/2011 03:52 PM, Thomas Gleixner wrote: > > On Tue, 13 Dec 2011, Avi Kivity wrote: > > > Run your guest with x2apic enabled, the timing will be very different. > > > > And what magic do I have to use to make that happen other than having > > x2apic support enabled in the kernel? Or do I need a certain kernel > > version for host and guest to make that work? > > With qemu, -cpu host or -cpu blah,+x2apic. kvm-tool does the equivalent
Well, that was a trace from qemu-kvm (your latest tree). Now with -cpu host it works and I get the same results as with kvm tool.
> of -cpu host, so I'm surprised it doesn't show up. x2apic has been > recognized by the guest for a long time (ce69a784; 2.6.32, I'll be > surprised if you have anything older than that on your machine). > > Does x2apic show up in your guest's /proc/cpuinfo?
Now it does :)
> > The whole APIC timer calibration and the back and forth > > conversion is definitely nothing which falls into the category of > > smart. > > APIC timer calibration is silly but it hasn't proven to be a real-world > problem.
Well, that depends on the world. The issue with that calibration is that it can be off and for a certain category of application it matters. Definitely not for the usual virt workload stuff. But saving cycles for highres/nohz enabled guests would be nice. Maybe I have a go when I find a some time.
Thanks,
tglx
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