On 02/05/2012 11:51 AM, Gleb Natapov wrote: > 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. I'm not happy about it either. > > > 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? I think the ioapic EOI is asynchronous wrt the core, yes? So the vcpu can just post the EOI broadcast on the apic-bus socketpair, waking up the thread handling the ioapic, and continue running. This trades off vcpu latency for using more host resources. -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
