Re: [libvirt-users] using more than 1 core by a virtual machine
Zvi Dubitzky
Email:dubi@il.ibm.com
IBM Haifa Research Laboratory Phone: +972-4-8296182
Haifa, 31905, ISRAEL
Osier Yang <jyang(a)redhat.com> wrote on 21/03/2011 10:27:07:
From: Osier Yang <jyang(a)redhat.com>
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 . Does the
latter appear only if
HW virtualization is active in the BIOS ?
thanks anyhow
Regards
Osier