[Engine-devel] CPU Overcommit Feature

[Andrew Cathrow]

----- Original Message -----
> From: "Dennis Jacobfeuerborn" <dennisml at conversis.de>
> To: engine-devel at 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 at redhat.com>
> >> To: "engine-devel" <engine-devel at ovirt.org>
> >> 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?

This is about the maximum number of vCPUs we can give to a VM.
If the machine has 32 Physical cores that are hyperthreaded then do we say the max number of vCPUs for a single VM is 32 or 64.


> 
> Regards,
>   Dennis
> 
> _______________________________________________
> Engine-devel mailing list
> Engine-devel at ovirt.org
> http://lists.ovirt.org/mailman/listinfo/engine-devel
>