On Fri, Apr 05, 2013 at 11:13:17AM +0200, Peter Krempa wrote:
On 04/05/13 10:37, Daniel P. Berrange wrote:
On Fri, Apr 05, 2013 at 12:11:31AM +0200, Peter Krempa wrote:
When setting processor count for a domain using the API libvirt enforced a maximum processor count, while it isn't enforced when taking the XML path.
This patch removes the check to match the API.
Do you mean s/API/XML/ here ?
Indeed.
I'm not sure whether removing this check is a good idea. Should we not instead make the guest startup code also validate max CPU count when generating the CLI args ?
Well, I don't think so. Adding the check to the CLI generator would introduce more problems than it would solve:
1) chicken and egg problem: we can't use the new QMP query-cpu-max command as we need a running qemu for this and in order to start a qemu you already need to provide the desired number of cpus:
$ qemu-system-x86_64 -smp 256 -M pc -S --monitor stdio Unsupported number of maxcpus $ qemu-system-x86_64 -smp 255 -M pc -S --monitor stdio QEMU 1.4.50 monitor - type 'help' for more information (qemu) info cpu_max Maximum number of CPUs is 255 (qemu) quit $
2) qemuGetMaxVCPUs() is obsolete and doesn't report apropriate numbers. For non-kvm guests this would limit us to 16 cpus per guest and for kvm guests it depends if the kernel supports the KVM_CAP_MAX_VCPUS ioctl (introduced in linux-3.2) and reports a correct value or we return the recommended value of processors (KVM_CAP_NR_VCPUS ioctl) that is hardcoded to 160. If neither of the ioctls is supported, 4 will be returned as the maximum count (according to kernel docs).
qemuGetMaxVCPUs(virConnectPtr conn ATTRIBUTE_UNUSED, const char *type) { if (!type) return 16;
if (STRCASEEQ(type, "qemu")) return 16;
if (STRCASEEQ(type, "kvm")) return kvmGetMaxVCPUs();
if (STRCASEEQ(type, "kqemu")) return 1;
...
I don't see a way how we could reliably determine the maximum for a guest before we start it and it doesn't make sense to start it to find out. I think we should just remove the check and let qemu handle the limit.
Ok, that makes sense now. Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|