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=-10.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 68D21C433E0 for ; Tue, 12 Jan 2021 12:55:23 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id EA0BC2310F for ; Tue, 12 Jan 2021 12:55:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EA0BC2310F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=GeYh2lnkAEFtyf4IYQ9j4kFNPyiP9nRRLsm3GtTE9Hk=; b=0t7ePSm+IUiVBCdT4tApavvT3 FE+Q7fNzG2Zpxu1naRV7jmEFtwqJcpGzO0CED+N8j1gePGu/55n9OMu0XRDNKrjxJfQi9q3OMQEo9 O52y5E5zYJQY1miQX/sXyRFrmnuSMNApSwZWmiz7O53Cj/78XP7p0P/hPSj1O+ixIf6wlCAyOZZ7w LbZsJ6iwLrbkHdTIdW1PdOal8CeR0lmYUC15MpmV4M5WvJPrto75786XJ91mseTkwzzZVTX2qtzy8 /ffmgJKgbc9FsQdRIC+LH/QEFrQ4sG7ntRLAwvu0D5/ciiJaoAJD5KyDvgzGrJWiwojMwiuiqzpnc TUAnrox+g==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kzJBA-0007pq-Tb; Tue, 12 Jan 2021 12:53:45 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kzJB6-0007nc-Hd for linux-arm-kernel@lists.infradead.org; Tue, 12 Jan 2021 12:53:41 +0000 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 E38E71042; Tue, 12 Jan 2021 04:53:32 -0800 (PST) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C85B43F66E; Tue, 12 Jan 2021 04:53:27 -0800 (PST) Subject: Re: [RFC PATCH v3 0/2] scheduler: expose the topology of clusters and add cluster scheduler To: "Song Bao Hua (Barry Song)" , Morten Rasmussen , Tim Chen References: <20210106083026.40444-1-song.bao.hua@hisilicon.com> <737932c9-846a-0a6b-08b8-e2d2d95b67ce@linux.intel.com> <20210108151241.GA47324@e123083-lin> From: Dietmar Eggemann Message-ID: Date: Tue, 12 Jan 2021 13:53:26 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210112_075340_743667_E5204959 X-CRM114-Status: GOOD ( 24.78 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "juri.lelli@redhat.com" , "mark.rutland@arm.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "bsegall@google.com" , "xuwei \(O\)" , "will@kernel.org" , "vincent.guittot@linaro.org" , "aubrey.li@linux.intel.com" , "linux-acpi@vger.kernel.org" , "mingo@redhat.com" , "mgorman@suse.de" , "valentin.schneider@arm.com" , "lenb@kernel.org" , "linuxarm@openeuler.org" , "rostedt@goodmis.org" , "Zengtao \(B\)" , Jonathan Cameron , "linux-arm-kernel@lists.infradead.org" , "gregkh@linuxfoundation.org" , "rjw@rjwysocki.net" , "linux-kernel@vger.kernel.org" , "sudeep.holla@arm.com" , "tiantao \(H\)" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 08/01/2021 22:30, Song Bao Hua (Barry Song) wrote: > >> -----Original Message----- >> From: Morten Rasmussen [mailto:morten.rasmussen@arm.com] >> Sent: Saturday, January 9, 2021 4:13 AM >> To: Tim Chen >> Cc: Song Bao Hua (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 ; >> 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; xuwei (O) ; Zengtao (B) >> ; tiantao (H) >> Subject: Re: [RFC PATCH v3 0/2] scheduler: expose the topology of clusters and >> add cluster scheduler >> >> 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? > > Morten, this is not true. > > we are both actually looking for the same behavior. My patch also > has done the exact same behavior of spreading with Tim's patch. That's the case for the load-balance path because of the extra Sched Domain (SD) (CLS/MC_L2) below MC. But in wakeup you add code which leads to a different packing strategy. It looks like that Tim's workload (SPECrate mcf) shows a performance boost solely because of the changes the additional MC_L2 SD introduces in load balance. The wakeup path is unchanged, i.e. llc-packing. IMHO we have to carefully distinguish between packing vs. spreading in wakeup and load-balance here. > Considering the below two cases: > Case 1. we have two tasks without any relationship running in a system with 2 clusters and 8 cpus. > > Without the sched_domain of cluster, these two tasks might be put as below: > +-------------------+ +-----------------+ > | +----+ +----+ | | | > | |task| |task| | | | > | |1 | |2 | | | | > | +----+ +----+ | | | > | | | | > | cluster1 | | cluster2 | > +-------------------+ +-----------------+ > With the sched_domain of cluster, load balance will spread them as below: > +-------------------+ +-----------------+ > | +----+ | | +----+ | > | |task| | | |task| | > | |1 | | | |2 | | > | +----+ | | +----+ | > | | | | > | cluster1 | | cluster2 | > +-------------------+ +-----------------+ > > Then task1 and tasks2 get more cache and decrease cache contention. > They will get better performance. > > That is what my original patch also can make. And tim's patch > is also doing. Once we add a sched_domain, load balance will > get involved. > > > Case 2. we have 8 tasks, running in a system with 2 clusters and 8 cpus. > But they are working in 4 groups: > Task1 wakes up task4 > Task2 wakes up task5 > Task3 wakes up task6 > Task4 wakes up task7 > > With my changing in select_idle_sibling, the WAKE_AFFINE mechanism will > try to put task1 and 4, task2 and 5, task3 and 6, task4 and 7 in same clusters rather > than putting all of them in the random one of the 8 cpus. However, the 8 tasks > are still spreading among the 8 cpus with my change in select_idle_sibling > as load balance is still working. > > +---------------------------+ +----------------------+ > | +----+ +-----+ | | +----+ +-----+ | > | |task| |task | | | |task| |task | | > | |1 | | 4 | | | |2 | |5 | | > | +----+ +-----+ | | +----+ +-----+ | > | | | | > | cluster1 | | cluster2 | > | | | | > | | | | > | +-----+ +------+ | | +-----+ +------+ | > | |task | | task | | | |task | |task | | > | |3 | | 6 | | | |4 | |8 | | > | +-----+ +------+ | | +-----+ +------+ | > +---------------------------+ +----------------------+ Your use-case (#tasks, runtime/period) seems to be perfectly crafted to show the benefit of your patch on your specific system (cluster-size = 4). IMHO, this extra infrastructure especially in the wakeup path should show benefits over a range of different benchmarks. > Let's consider the 3rd case, that one would be more tricky: > > task1 and task2 have close relationship and they are waker-wakee pair. > With my current patch, select_idle_sidling() wants to put them in one > cluster, load balance wants to put them in two clusters. Load balance will win. > Then maybe we need some same mechanism like adjusting numa imbalance: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/kernel/sched/fair.c?id=b396f52326de20 > if we permit a light imbalance between clusters, select_idle_sidling() > will win. And task1 and task2 get better cache affinity. This would look weird to allow this kind of imbalance on CLS (MC_L2) and NUMA domains but not on the MC domain for example. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel