[libvirt] [PATCH] qemu: match vcpu topology to maximum vcpu numbers.

[Guannan Ren]

On 05/29/2013 04:20 AM, Eric Blake wrote:
> On 05/28/2013 03:59 AM, Guannan Ren wrote:
>> For qemu, if the -smp N or the value of maxcpus is given, it define
>> the number of vcpu of guest whenever the vcpu topology is defined or
>> not. But if the -smp N and maxcpus are missing, the topology can
>> compute and define vcpus for guest automatically by math:
>>
>> vcpu number = sockets*cores*threads
>>
>> For libvirt, as <vcpu> is always mandatory, so we can ask topology
>> to match maximum vcpu numbers.
>> ---
>>   src/conf/domain_conf.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
>> index a9656af..ffdc6da 100644
>> --- a/src/conf/domain_conf.c
>> +++ b/src/conf/domain_conf.c
>> @@ -11815,10 +11815,10 @@ virDomainDefParseXML(xmlDocPtr xml,
>>               goto error;
>>   
>>           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.
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.


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.