From mboxrd@z Thu Jan 1 00:00:00 1970 From: jeremy.linton@arm.com (Jeremy Linton) Date: Wed, 6 Jun 2018 09:53:39 -0500 Subject: [PATCH] arm64: topology: Avoid checking numa mask for scheduler MC selection In-Reply-To: <20180606144444.GB8461@e105550-lin.cambridge.arm.com> References: <20180605190837.493505-1-jeremy.linton@arm.com> <20180606144444.GB8461@e105550-lin.cambridge.arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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.