From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 36E2B60767 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 S1752189AbeFFOxm (ORCPT + 25 others); Wed, 6 Jun 2018 10:53:42 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:41372 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751957AbeFFOxk (ORCPT ); Wed, 6 Jun 2018 10:53:40 -0400 Subject: Re: [PATCH] arm64: topology: Avoid checking numa mask for scheduler MC selection To: Morten Rasmussen 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 References: <20180605190837.493505-1-jeremy.linton@arm.com> <20180606144444.GB8461@e105550-lin.cambridge.arm.com> From: Jeremy Linton Message-ID: Date: Wed, 6 Jun 2018 09:53:39 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180606144444.GB8461@e105550-lin.cambridge.arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.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.