On Thu, Jul 20, 2017 at 03:03:25PM +0200, Wim ten Have wrote:
> On Thu, 20 Jul 2017 11:10:31 +0100
> "Daniel P. Berrange" <berrange@xxxxxxxxxx> wrote:
>
> > On Thu, Jul 20, 2017 at 11:29:26AM +0200, Wim Ten Have wrote:
> > > From: Wim ten Have <wim.ten.have@xxxxxxxxxx>
> > >
> > > The QEMU driver can erroneously allocate more vpus to a domain
> > > than there are cpus in the domain if the <numa> element is used
> > > to describe <cpu> element topology. Fix this by calculating
> > > the number of cpus described in the <numa> element of a <cpu>
> > > element and comparing it to the number of vcpus. If the number
> > > of vcpus is greater than the number of cpus, cap the number of
> > > vcpus to the number of cpus.
> > >
> > > This patch also adds a small libvirt documentation update under
> > > the "CPU Allocation" section.
> > >
> > > Signed-off-by: Wim ten Have <wim.ten.have@xxxxxxxxxx>
> > > ---
> > > docs/formatdomain.html.in | 9 ++++++++-
> > > src/conf/domain_conf.c | 14 +++++++++++---
> > > 2 files changed, 19 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
> > > index 07208ee..3c85307 100644
> > > --- a/docs/formatdomain.html.in
> > > +++ b/docs/formatdomain.html.in
> > > @@ -501,7 +501,14 @@
> > > <dt><code>vcpu</code></dt>
> > > <dd>The content of this element defines the maximum number of virtual
> > > CPUs allocated for the guest OS, which must be between 1 and
> > > - the maximum supported by the hypervisor.
> > > + the maximum supported by the hypervisor. If a <code>numa</code>
> > > + element is contained within the <code>cpu</code> element, the
> > > + number of virtual CPUs to be allocated is compared with the sum
> > > + of the <code>cpus</code> attributes across the <code>cell</code>
> > > + elements within the <code>numa</code> element. If the number of
> > > + virtual CPUs is greater than the sum of the <code>cpus</code>
> > > + attributes, the number of virtual CPUs is capped at sum of the
> > > + <code>cpus</code> attributes.
> > > <dl>
> > > <dt><code>cpuset</code></dt>
> > > <dd>
> > > diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
> > > index 958a5b7..73d7f4f 100644
> > > --- a/src/conf/domain_conf.c
> > > +++ b/src/conf/domain_conf.c
> > > @@ -3844,12 +3844,20 @@ virDomainDefPostParseMemory(virDomainDefPtr def,
> > > unsigned long long numaMemory = 0;
> > > unsigned long long hotplugMemory = 0;
> > >
> > > - /* Attempt to infer the initial memory size from the sum NUMA memory sizes
> > > - * in case ABI updates are allowed or the <memory> element wasn't specified */
> > > + /* Attempt to infer the initial memory size from the sum NUMA memory
> > > + * sizes in case ABI updates are allowed or the <memory> element
> > > + * wasn't specified. Also cap the vcpu count to the sum of NUMA cpus
> > > + * allocated for all nodes. */
> > > if (def->mem.total_memory == 0 ||
> > > parseFlags & VIR_DOMAIN_DEF_PARSE_ABI_UPDATE ||
> > > - parseFlags & VIR_DOMAIN_DEF_PARSE_ABI_UPDATE_MIGRATION)
> > > + parseFlags & VIR_DOMAIN_DEF_PARSE_ABI_UPDATE_MIGRATION) {
> > > + unsigned int numaVcpus = 0;
> > > +
> > > + if ((numaVcpus = virDomainNumaGetCPUCountTotal(def->numa)))
> > > + virDomainDefSetVcpus(def, numaVcpus);
> > > +
> > > numaMemory = virDomainNumaGetMemorySize(def->numa);
> > > + }
> >
> > AFAICT, this scenario is simply a user configuration mistake, and so we
> > should report an error message to them to fix it.
>
> Not to push but I think this is the correct way ... O:-).
>
> Ok, perhaps the documentation note/commit message should be slightly
> rewritten aswell as the altered comment on specific code section.
>
> The change is _NOT_ changing final guest provided 'maxvcpus' but
> 'vcpus' instead. This means that it adds the "current='#count'" under
> the vcpu element if such is less then vcpu 'maxvcpus' provided count.
> If equal there is no issue and if larger there is indeed a correct
> error message (exceptional condition).
>
> Imagine simpel domain description _WITHOUT_ <numa> and below <vcpu>
> element description;
>
> <vcpu placement='static' current='4'>16</vcpu>
>
> This nicely creates a guest with 4 domain CPUs added, where the
> administrator can "hot-add" an additional 12 CPUs making the full
> 'maxvcpus' defined 16. "hot-add" by virsh;
>
> virsh # setvcpus kvm26 16
>
> Without the fix under former <numa> domain description libvirt would
> bring whole '16' vcpus to the guest, and if there was a current value
> given all by current on top of the <numa> <cell ... to NUMA-node0
> for that matter :-( so wrong;
>
> <vcpu placement='static'>16</vcpu>
> ..
> <numa>
> <cell id='0' cpus='0' memory='262144' unit='KiB'/>
> <cell id='1' cpus='1' memory='262144' unit='KiB'/>
> <cell id='2' cpus='2' memory='262144' unit='KiB'/>
> <cell id='3' cpus='3' memory='262144' unit='KiB'/>
> </numa>
This is saying that we have 16 CPU sockets, but you're only
assigning NUMA affinity to 4 of the sockets. IMHO that is
a configuration mistake. All 16 CPU sockets need to have
affinity assigned, so that when they're later brought online
they can be placed suitably on the host.
>
> With the fix, its post configuration action will now nicely rewrite
> the <vcpu ... current='#count'> element as shown below;
>
> <vcpu placement='static' current='4'>16</vcpu>
> ..
> <numa>
> <cell id='0' cpus='0' memory='262144' unit='KiB'/>
> <cell id='1' cpus='1' memory='262144' unit='KiB'/>
> <cell id='2' cpus='2' memory='262144' unit='KiB'/>
> <cell id='3' cpus='3' memory='262144' unit='KiB'/>
> </numa>
IMHO that is still just as broken as the previous config,
because it isn't saying how to set affinity on the remaining
12 vCPUs that can be brought online.
>
> In case "current='#count'" description is given where it does not
> match the <numa> <cell ... #cpus> count then such is corrected to
> cap the sum of all <numa> <cell ... #cpus>.
> Perhaps that occurance should be rejected with an error message, then
> such is not exceeding the domain administrators written <vcpu> 'maxvcpus'
> element being '16' within my example above. That is a hard limit and
> of course rejected with an error.
>
> I will not argue further ... O:-) I'll wait and if it is a _NO_ then
> it is a _NO_!
Regards,
Daniel
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