My virtual machine xml file has<vcpu>2</vcpu> clause while the host has 2 physical cpus (cores). Is this enough to cause a VM running 2 endless loop threads to use the 2 cores ? In my case the VM running reports (cat /roc/cpuinfo) that it has 2 vcpus but it uses only 1 core (at a time) because the 'top' at the host shows 100%cpu (out of total 200%) used by the endless loop application Also virsh vcpuinfo<vm> shows only 1 CPU and 1 vcpu

Zvi Dubitzky Email:dubi@il.ibm.com IBM Haifa Research Laboratory Phone: +972-4-8296182 Haifa, 31905, ISRAEL Osier Yang&lt;jyang(a)redhat.com&gt; wrote on 21/03/2011 10:27:07: > From: Osier Yang&lt;jyang(a)redhat.com&gt; > To: Zvi Dubitzky/Haifa/IBM@IBMIL > Cc: libvirt-users(a)redhat.com > Date: 21/03/2011 10:27 > Subject: Re: [libvirt-users] using more than 1 core by a virtual machine > > 于 2011年03月17日 02:04, Zvi Dubitzky 写道: >> My virtual machine xml file has<vcpu>2</vcpu> clause while the host has >> 2 physical cpus (cores). >> Is this enough to cause a VM running 2 endless loop threads to use the 2 >> cores ? >> In my case the VM running reports (cat /roc/cpuinfo) that it has 2 vcpus >> but it uses only 1 core (at a time) because >> the 'top' at the host shows 100%cpu (out of total 200%) used by the >> endless loop application >> Also virsh vcpuinfo<vm> shows only 1 CPU and 1 vcpu > > Is it really only 1 vcpu is showed? it should be two, that's > strange if you specified two vcpus, but only 1 is showed. > and by default, if you don't specify "cpuset" in<vcpu>, it uses > all the physical cpus, if I'm right, so you should be able to > see something like: > > CPU Affinity: yy > > Could you try specify "cpuset" explicitly like: > > <vcpu cpuset="0,1">2</vcpu> > > And see what it happens? > NO. There 2 vcpus in the VM screen . I pasted only one of them . yes there is PU Affinity: yy anyhow in 'virsh vcpuinfo<domain> even before fixing the problem as below. I solved the problem : The BIOS did not have VT enabled although multiprocessing item was already enabled in the BIOS and also some item called "virtualization " was already enabled . But that was not enough : I also had to drop the following clause from the VM xml file: '<emulator>/usr/local/bin/qemu-system-x86_64</emulator>' Anyhow: I do not understand why using multicore under a VM is dependent on the VT enabled Now the 'top' utility (at the host) shows qemu-kvm is the running process instead of qemu-system-x86_64 as before the fix . On the another Debian system I did not have to drop the<emulator> clause from the xml and the VM was still using all the cores though ! But the libvirt at the Debian was newer (0.8.6) while the fedora14 was running libvirt 0.8.3 Do you know what is exactly qemu-system-x86_64 vs. qemu-kvm .

latter appear only if HW virtualization is active in the BIOS ?