On Thu, 20 Jul 2017 11:10:31 +0100 "Daniel P. Berrange" <berrange@redhat.com> wrote:
On Thu, Jul 20, 2017 at 11:29:26AM +0200, Wim Ten Have wrote:
From: Wim ten Have <wim.ten.have@oracle.com>
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@oracle.com> --- 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> 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> 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, - Wim.