From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org C9CFB607CF Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752204AbeFFPHw (ORCPT + 25 others); Wed, 6 Jun 2018 11:07:52 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:41590 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751891AbeFFPHu (ORCPT ); Wed, 6 Jun 2018 11:07:50 -0400 Date: Wed, 6 Jun 2018 16:07:45 +0100 From: Morten Rasmussen To: Jeremy Linton Cc: Sudeep.Holla@arm.com, Will.Deacon@arm.com, Catalin.Marinas@arm.com, Robin.Murphy@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, geert@linux-m68k.org, linux-acpi@vger.kernel.org, ard.biesheuvel@linaro.org Subject: Re: [PATCH] arm64: topology: Avoid checking numa mask for scheduler MC selection Message-ID: <20180606150745.GC8461@e105550-lin.cambridge.arm.com> References: <20180605190837.493505-1-jeremy.linton@arm.com> <20180606144444.GB8461@e105550-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.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