[libvirt-users] using more than 1 core by a virtual machine
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 any idea ? thanks Zvi Dubitzky Email:dubi@il.ibm.com
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? Regards Osier
From: Osier Yang <jyang@redhat.com> To: Zvi Dubitzky/Haifa/IBM@IBMIL Cc: libvirt-users@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
Zvi Dubitzky Email:dubi@il.ibm.com IBM Haifa Research Laboratory Phone: +972-4-8296182 Haifa, 31905, ISRAEL Osier Yang <jyang@redhat.com> wrote on 21/03/2011 10:27:07: 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
于 2011年03月21日 16:49, Zvi Dubitzky 写道:
Zvi Dubitzky Email:dubi@il.ibm.com IBM Haifa Research Laboratory Phone: +972-4-8296182 Haifa, 31905, ISRAEL
Osier Yang<jyang@redhat.com> wrote on 21/03/2011 10:27:07:
From: Osier Yang<jyang@redhat.com> To: Zvi Dubitzky/Haifa/IBM@IBMIL Cc: libvirt-users@redhat.com Date: 21/03/2011 10:27 Subject: Re: [libvirt-users] using more than 1 core by a virtual machine
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
于 2011年03月17日 02:04, Zvi Dubitzky 写道: 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 .
Simpley speaking, qemu-kvm is with kvm support, while qemu-system-x86-64 is not. Does the
latter appear only if HW virtualization is active in the BIOS ?
Not sure what your exact meaning, but I guess you mean it appears in domain xml. If so: libvirt contruct the capability of qemu driver when libvirtd starts, if your host doesn't enable VT support, then kvm module is not loaded, libvirt inspects if "/dev/kvm" is accessiable to determine whether to use "qemu-kvm" as emulator in the capability xml or not. That's why it's not <emulator>/usr/libexec/qemu-kvm</emulator> in your domain xml. It's not the detailed explaination, but simply makes sense for you. To see the qemu guest capabilities your host supports: # virsh -c qemu:///system capabilities And anyway, I don't think multicore for VM relates with the emulator, if qemu-kvm is used, vcpus are virtualized by KVM, if qemu-system-x86_64 is used, they are emulated. Regards Osier
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