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    SubjectRe: [patch 0/3] kvm tool: Serial emulation overhaul
    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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