Re: [RFC] Next gen kvm api
From: Avi Kivity
Date: Sun Feb 05 2012 - 04:45:11 EST
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
No, but older guests may have reduced performance in some workloads
(e.g. RHEL4 gettimeofday() intensive workloads).
> 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,
error compiling committee.c: too many arguments to function
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