Re: [Engine-devel] CPU Overcommit Feature

From: "Dennis Jacobfeuerborn" <dennisml(a)conversis.de&gt; To: engine-devel(a)ovirt.org Sent: Tuesday, December 18, 2012 12:30:34 PM Subject: Re: [Engine-devel] CPU Overcommit Feature On 12/17/2012 07:13 PM, Simon Grinberg wrote: > > > ----- Original Message ----- >> From: "Greg Padgett" <gpadgett(a)redhat.com&gt; >> To: "engine-devel" <engine-devel(a)ovirt.org&gt; >> Sent: Monday, December 17, 2012 4:37:57 PM >> Subject: [Engine-devel] CPU Overcommit Feature >> >> Hi, >> >> I've been working on a feature to allow CPU Overcommitment of >> hosts >> in a >> cluster. This first stage allows the engine to consider host cpu >> threads >> as cores for the purposes of VM resource allocation. >> >> This wiki page has further details, your comments are welcome! >> http://www.ovirt.org/Features/cpu_overcommit > > Basically looking good. > Hyperthread though is vendor specific. > > For AMD it's Clustered Multi-Thread while for Intel it's > Hyper-Thread > Official name is simultaneous multithreading (SMT) but no one > outside of the academy will recognize that. > > in libvirt if I read it right it's <attribute > name='thread_siblings'> > > So why not just call it threads. > We'll have cpuSockets, cpiCores, and cpuThreads, should be clear > when in CPU context. > > In the GUI just change hyperthreads to CPU threads. While in the > tool tip explain that it's either AMD Clustered Multi-Thread or > Intel Hyperthread Does this affect only the number of potential vCpus for the guests or does this also have an impact on the actual scheduling? So far I always disabled HT out of fear that a 2 vCpu guest might actually be scheduled to run in 2 threads of the same core but now I'm not so sure anymore. In the HT case does KVM know that two threads belong to the same core and will it only schedule its vCpus on distinct cores? Is there some documentation about this somewhere?

Regards, Dennis _______________________________________________ Engine-devel mailing list Engine-devel(a)ovirt.org http://lists.ovirt.org/mailman/listinfo/engine-devel