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 X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 21441C433E0 for ; Fri, 8 Jan 2021 15:13:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE82223998 for ; Fri, 8 Jan 2021 15:13:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726863AbhAHPNi (ORCPT ); Fri, 8 Jan 2021 10:13:38 -0500 Received: from foss.arm.com ([217.140.110.172]:52824 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725806AbhAHPNi (ORCPT ); Fri, 8 Jan 2021 10:13:38 -0500 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 24E61ED1; Fri, 8 Jan 2021 07:12:52 -0800 (PST) Received: from e123083-lin (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 88CFA3F70D; Fri, 8 Jan 2021 07:12:47 -0800 (PST) Date: Fri, 8 Jan 2021 16:12:41 +0100 From: Morten Rasmussen To: Tim Chen Cc: Barry Song , valentin.schneider@arm.com, catalin.marinas@arm.com, will@kernel.org, rjw@rjwysocki.net, vincent.guittot@linaro.org, lenb@kernel.org, gregkh@linuxfoundation.org, jonathan.cameron@huawei.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, mark.rutland@arm.com, sudeep.holla@arm.com, aubrey.li@linux.intel.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linuxarm@openeuler.org, xuwei5@huawei.com, prime.zeng@hisilicon.com, tiantao6@hisilicon.com Subject: Re: [RFC PATCH v3 0/2] scheduler: expose the topology of clusters and add cluster scheduler Message-ID: <20210108151241.GA47324@e123083-lin> References: <20210106083026.40444-1-song.bao.hua@hisilicon.com> <737932c9-846a-0a6b-08b8-e2d2d95b67ce@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <737932c9-846a-0a6b-08b8-e2d2d95b67ce@linux.intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Thu, Jan 07, 2021 at 03:16:47PM -0800, Tim Chen wrote: > On 1/6/21 12:30 AM, Barry Song wrote: > > ARM64 server chip Kunpeng 920 has 6 clusters in each NUMA node, and each > > cluster has 4 cpus. All clusters share L3 cache data while each cluster > > has local L3 tag. On the other hand, each cluster will share some > > internal system bus. This means cache is much more affine inside one cluster > > than across clusters. > > There is a similar need for clustering in x86. Some x86 cores could share L2 caches that > is similar to the cluster in Kupeng 920 (e.g. on Jacobsville there are 6 clusters > of 4 Atom cores, each cluster sharing a separate L2, and 24 cores sharing L3). > Having a sched domain at the L2 cluster helps spread load among > L2 domains. This will reduce L2 cache contention and help with > performance for low to moderate load scenarios. IIUC, you are arguing for the exact opposite behaviour, i.e. balancing between L2 caches while Barry is after consolidating tasks within the boundaries of a L3 tag cache. One helps cache utilization, the other communication latency between tasks. Am I missing something? IMHO, we need some numbers on the table to say which way to go. Looking at just benchmarks of one type doesn't show that this is a good idea in general. Morten