From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2A5EBC433EF for ; Fri, 20 May 2022 12:34:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349441AbiETMd7 (ORCPT ); Fri, 20 May 2022 08:33:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53474 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349362AbiETMde (ORCPT ); Fri, 20 May 2022 08:33:34 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C2D8E163F6C for ; Fri, 20 May 2022 05:33:31 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3916A1477; Fri, 20 May 2022 05:33:31 -0700 (PDT) Received: from [172.29.1.145] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 629363F718; Fri, 20 May 2022 05:33:28 -0700 (PDT) Message-ID: <26f39a9d-1a02-b77d-5c89-88a1fb0e4eac@arm.com> Date: Fri, 20 May 2022 14:33:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [PATCH v2 3/8] arch_topology: Set cluster identifier in each core/thread from /cpu-map Content-Language: en-US To: Ionela Voinescu , Sudeep Holla Cc: Atish Patra , linux-kernel@vger.kernel.org, Atish Patra , Vincent Guittot , Morten Rasmussen , Qing Wang , linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, Rob Herring References: <20220518093325.2070336-1-sudeep.holla@arm.com> <20220518093325.2070336-4-sudeep.holla@arm.com> From: Dietmar Eggemann In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/05/2022 18:55, Ionela Voinescu wrote: > Hi, > > As said before, this creates trouble for CONFIG_SCHED_CLUSTER=y. > The output below is obtained from Juno. > > When cluster_id is populated, a new CLS level is created by the scheduler > topology code. In this case the clusters in DT determine that the cluster > siblings and llc siblings are the same so the MC scheduler domain will > be removed and, for Juno, only CLS and DIE will be kept. [...] > To be noted that we also get a new flag SD_PREFER_SIBLING for the CLS > level that is not appropriate. We usually remove it for the child of a > SD_ASYM_CPUCAPACITY domain, but we don't currently redo this after some > levels are degenerated. This is a fixable issue. > > But looking at the bigger picture, a good question is what is the best > thing to do when cluster domains and llc domains span the same CPUs? > > Possibly it would be best to restrict clusters (which are almost an > arbitrary concept) to always span a subset of CPUs of the llc domain, > if llc siblings can be obtained? If those clusters are not properly set > up in DT to respect this condition, cluster_siblings would need to be > cleared (or set to the current CPU) so the CLS domain is not created at > all. > > Additionally, should we use cluster information from DT (cluster_id) to > create an MC level if we don't have llc information, even if > CONFIG_SCHED_CLUSTER=n? > > I currently don't have a very clear picture of how cluster domains and > llc domains would "live" together in a variety of topologies. I'll try > other DT topologies to see if there are others that can lead to trouble. This would be an issue. Depending on CONFIG_SCHED_CLUSTER we would get two different systems from the viewpoint of the scheduler. To me `cluster_id/_sibling` don't describe a certain level of CPU grouping (e.g. one level above core or one level below package). They were introduced to describe one level below LLC (e.g. Kunpeng920 L3 (24 CPUs LLC) -> L3 tag (4 CPUs) or x86 Jacobsville L3 -> L2), (Commit ^^^^^^ ^^ c5e22feffdd7 ("topology: Represent clusters of CPUs within a die")). The Ampere Altra issue already gave us a taste of the possible issues of this definition, commit db1e59483dfd ("topology: make core_mask include at least cluster_siblings"). If we link `cluster_id/_sibling` against (1. level) cpu-map cluster nodes plus using llc and `cluster_sibling >= llc_sibling` we will run into these issues.