[ovirt-devel] CPU sockets, threads, cores and NUMA

[Francesco Romani]

----- Original Message -----
> From: "Martin Polednik" <mpolednik at redhat.com>
> To: devel at ovirt.org
> Sent: Thursday, December 10, 2015 4:07:57 PM
> Subject: [ovirt-devel] CPU sockets, threads, cores and NUMA

> It does fail to provide us with information that can be used in
> ppc64le environment, where for POWER8 we want to run the host without
> SMT while VMs would have multiple CPUs assigned. There are various
> configurations of so-called subcores in POWER8, where each CPU core
> can contain 1, 2 or 4 subcores.

What are those subcores? Does this subcore concept map on something like
SMT on x86_64? Or is this an hardware concept (mind goes to the
AMD's bulldozer modules)

> This configuration must be taken in
> consideration as given e.g. 160 threads overall, it is possible to run
> either 20 VMs in smt8 mode, 40 VMs in smt4 mode or 80 VMs in smt2
> mode.

Could you elaborate a bit more about the se smtX modes and how they
play with threads and cores?

> We have to report either the total number of threads OR just the
> threadsPerCore setting, so the users know how many "CPUs" should be
> assigned to machines for optimal performance.

Which options is best for ppc, if there is any difference?


bests,

-- 
Francesco Romani
RedHat Engineering Virtualization R & D
Phone: 8261328
IRC: fromani