Re: [PATCH] arm64: topology: Avoid checking numa mask for scheduler MC selection
From: Jeremy Linton
Date: Wed Jun 06 2018 - 10:53:45 EST
On 06/06/2018 09:44 AM, Morten Rasmussen wrote:
On Tue, Jun 05, 2018 at 02:08:37PM -0500, Jeremy Linton wrote:
The numa mask subset check has problems if !CONFIG_NUMA, over hotplug
operations or during early boot. Lets disable the NUMA siblings checks
for the time being, as NUMA in socket machines have LLC's that will
assure that the scheduler topology isn't "borken".
Could we add an explanation why the numa node mask check is needed in
the first place. >
IIUC, we have the check in case the LLC is shared across numa nodes as
this would cause core_siblings > cpumask_of_node() which breaks the
scheduler topology.
Yes, that sounds like a good idea, my comments probably assume that the
reader has been part of these conversations.
While sharing LLC across numa nodes seems quite unusual, I think it is
allowed by ACPI. Those systems might already be broken before, so might
not change anything. It is just worth noting why the check should be
added back later.
Right, there isn't anything in ACPI that dictates a system topology
restriction like this. Given that other architectures have built
machines with large directory caches that span numa nodes the check was
a safety measure.