so qemu exposes multiple processors to the guest os by having multiple vCPUs. and it realizes the multiple vCPUs by either using RR on a single host cpu (qemu ) or using multiple host cpus (kvm).
Thanks Xin 2011/11/8 Stefan Hajnoczi <stefa...@gmail.com>: > On Tue, Nov 8, 2011 at 12:10 PM, 陳韋任 <che...@iis.sinica.edu.tw> wrote: >> On Tue, Nov 08, 2011 at 08:04:44PM +0800, 陳韋任 wrote: >>> > I am wondering that when one uses qemu with kvm. How many cores are >>> > exposed and available to the guest os ( assuming the host has 4 cores >>> > ). is this configurable ? >>> >>> QEMU provides "-smp" option, but those virtual cpus are scheduled in >>> round-robin fashion. In other words, it's not real parallelism. I don't >>> know if there is any difference with kvm enabled. >> >> IIRC, kvm uses QEMU for device emulation only. Those virtual cpus are >> ran on physical cpus simultaneously. > > Right, qemu -enable-kvm will run a thread for each vCPU. So you get > true SMP parallelism. > > QEMU without KVM mode, on the other hand, does round-robin scheduling > of vCPUs and does not take advantage of multiprocessor hosts. > > Stefan >