On 05/28/2013 07:32 PM, Guannan Ren wrote:
if (def->cpu->sockets && - def->maxvcpus > + def->maxvcpus != def->cpu->sockets * def->cpu->cores * def->cpu->threads) { virReportError(VIR_ERR_XML_DETAIL, "%s", - _("Maximum CPUs greater than topology limit")); + _("Topology limit does not match maximum CPUs"));
Is this going to reject XML that was previously accepted? Is there a bugzilla showing what happens if this patch is not incorporated? I'm worried about introducing an unintentional regression if we include this in 1.0.6 without more justification.
Yes, it make the cpu topology limit setting more strict.
I'm okay with making things more strict, if it makes sense. But isn't it feasible to support a topology that has more slots than the maximum? That is, since a bare metal machine can have two sockets but only populate one, why can't a virtual machine have 2 sockets but set a max vcpu of 1 so that only one socket can be populated? Does qemu itself enforce that there be a match? That's why I'm worried about enforcing that the user can't have a mismatch between maxvcpus vs. topology, if they specify both. I'm also worried that this check might fire if the user specifies only topology or only maxvcpus; I want to make sure that we only do the sanity checking if both numbers are provided.
Alternatively, we can add more comments for <topology> to make it clear that <vcpu> decide the number of vcpus, the sockets*cores*threads had better be equal to vcpu numbers.
If there is a problem with a mismatch, then we should document that a match is required, and fail on mismatch. Merely documenting that a match is required without enforcing it is too weak; and enforcing it without documentation is a disservice. I haven't ruled out enforcing a match, but want to make sure that we aren't artificially crippling something that might prove useful in reality, when compared with what bare-metal setups can provide.
The bz:https://bugzilla.redhat.com/show_bug.cgi?id=880017
Description of problem: libvirt should check if vcpu topology is right. If the wrong vcpu topology is given in xml , the wrong arguments also be passed to qemu-kvm.
vcpu number = sockets*cores*threads
Steps to Reproduce: 1.# virsh start vm Domain vm started
2.# virsh dumpxml vm <domain type='kvm' id='104'> ....... <vcpu placement='static'>4</vcpu> ...... <cpu> <topology sockets='1' cores='4' threads='2'/> </cpu>
3.# ps -ef|grep qemu-kvm qemu 21296 1 14 16:41 ? 00:00:17 /usr/libexec/qemu-kvm -name vm -S -M rhel6.4.0 -enable-kvm -m 1024 -smp 4,sockets=1,cores=4,threads=2 ......
Actual results: Wrong vcpu topology can be given in xml and passed to qemu-kvm
Expected results: libvirt should check if vcpu topology is right.
-- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org