From mboxrd@z Thu Jan 1 00:00:00 1970 From: morten.rasmussen@arm.com (Morten Rasmussen) Date: Wed, 6 Jun 2018 16:07:45 +0100 Subject: [PATCH] arm64: topology: Avoid checking numa mask for scheduler MC selection In-Reply-To: References: <20180605190837.493505-1-jeremy.linton@arm.com> <20180606144444.GB8461@e105550-lin.cambridge.arm.com> Message-ID: <20180606150745.GC8461@e105550-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Jun 06, 2018 at 09:53:39AM -0500, Jeremy Linton wrote: > 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. Agreed, it seems that another architecture has recently merged support for that: 1340ccfa9a9a