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    SubjectRe: [RFC] Next gen kvm api
    On Sun, Feb 05, 2012 at 11:44:43AM +0200, Avi Kivity wrote:
    > On 02/05/2012 11:37 AM, Gleb Natapov wrote:
    > > On Thu, Feb 02, 2012 at 06:09:54PM +0200, Avi Kivity wrote:
    > > > Device model
    > > > ------------
    > > > Currently kvm virtualizes or emulates a set of x86 cores, with or
    > > > without local APICs, a 24-input IOAPIC, a PIC, a PIT, and a number of
    > > > PCI devices assigned from the host. The API allows emulating the local
    > > > APICs in userspace.
    > > >
    > > > The new API will do away with the IOAPIC/PIC/PIT emulation and defer
    > > > them to userspace. Note: this may cause a regression for older guests
    > > > that don't support MSI or kvmclock. Device assignment will be done
    > > > using VFIO, that is, without direct kvm involvement.
    > > >
    > > So are we officially saying that KVM is only for modern guest
    > > virtualization?
    >
    > No, but older guests may have reduced performance in some workloads
    > (e.g. RHEL4 gettimeofday() intensive workloads).
    >
    Reduced performance is what I mean. Obviously old guests will continue working.

    > > Also my not so old host kernel uses MSI only for NIC.
    > > SATA and USB are using IOAPIC (though this is probably more HW related
    > > than kernel version related).
    >
    > For devices emulated in userspace, it doesn't matter where the IOAPIC
    > is. It only matters for kernel provided devices (PIT, assigned devices,
    > vhost-net).
    >
    What about EOI that will have to do additional exit to userspace for each
    interrupt delivered?

    --
    Gleb.


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