Re: [ovirt-devel] CPU sockets, threads, cores and NUMA
----- Original Message -----
From: "Martin Polednik" <mpolednik(a)redhat.com>
To: devel(a)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