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 715E8C7EE23 for ; Thu, 8 Jun 2023 06:46:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234950AbjFHGqC (ORCPT ); Thu, 8 Jun 2023 02:46:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35038 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234886AbjFHGqA (ORCPT ); Thu, 8 Jun 2023 02:46:00 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E738A2132 for ; Wed, 7 Jun 2023 23:45:58 -0700 (PDT) Received: from canpemm500009.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4QcF6D3lYvztQVD; Thu, 8 Jun 2023 14:43:32 +0800 (CST) Received: from [10.67.102.169] (10.67.102.169) by canpemm500009.china.huawei.com (7.192.105.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Thu, 8 Jun 2023 14:45:55 +0800 CC: , Peter Zijlstra , , , , , , , , , , , , , , , , , , , <21cnbao@gmail.com>, , , Barry Song , Tim Chen , Ricardo Neri , Len Brown Subject: Re: [PATCH v8 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path To: Chen Yu References: <20230530070253.33306-1-yangyicong@huawei.com> <20230530070253.33306-3-yangyicong@huawei.com> <20230530115527.GC156198@hirez.programming.kicks-ass.net> <8fcba5d4-eea5-d7c4-2bf7-482321b333b7@huawei.com> From: Yicong Yang Message-ID: <85e29dd8-60f6-1e84-b3e4-061e5a2a0037@huawei.com> Date: Thu, 8 Jun 2023 14:45:54 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.102.169] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To canpemm500009.china.huawei.com (7.192.105.203) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/6/8 11:26, Chen Yu wrote: > On 2023-05-31 at 16:21:00 +0800, Yicong Yang wrote: >> On 2023/5/30 22:39, Yicong Yang wrote: >>> On 2023/5/30 19:55, Peter Zijlstra wrote: >>>> On Tue, May 30, 2023 at 03:02:53PM +0800, Yicong Yang wrote: >>>> >>>>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>>>> index 373ff5f55884..b8c129ed8b47 100644 >>>>> --- a/kernel/sched/fair.c >>>>> +++ b/kernel/sched/fair.c >>>>> @@ -6994,6 +6994,30 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool >>>>> } >>>>> } >>>>> >>>>> + if (static_branch_unlikely(&sched_cluster_active)) { >>>>> + struct sched_domain *sdc = rcu_dereference(per_cpu(sd_cluster, target)); >>>>> + >>>>> + if (sdc) { >>>>> + for_each_cpu_wrap(cpu, sched_domain_span(sdc), target + 1) { >>>>> + if (!cpumask_test_cpu(cpu, cpus)) >>>>> + continue; >>>>> + >>>>> + if (has_idle_core) { >>>>> + i = select_idle_core(p, cpu, cpus, &idle_cpu); >>>>> + if ((unsigned int)i < nr_cpumask_bits) >>>>> + return i; >>>>> + } else { >>>>> + if (--nr <= 0) >>>>> + return -1; >>>>> + idle_cpu = __select_idle_cpu(cpu, p); >>>>> + if ((unsigned int)idle_cpu < nr_cpumask_bits) >>>>> + return idle_cpu; >>>>> + } >>>>> + } >>>>> + cpumask_andnot(cpus, cpus, sched_domain_span(sdc)); >>>>> + } >>>>> + } >>>> >>>> Would not this: >>>> >>>> --- a/kernel/sched/fair.c >>>> +++ b/kernel/sched/fair.c >>>> @@ -6994,6 +6994,29 @@ static int select_idle_cpu(struct task_s >>>> } >>>> } >>>> >>>> + if (static_branch_unlikely(&sched_cluster_active)) { >>>> + struct sched_group *sg = sd->groups; >>>> + if (sg->flags & SD_CLUSTER) { >>>> + for_each_cpu_wrap(cpu, sched_group_span(sg), target+1) { >>>> + if (!cpumask_test_cpu(cpu, cpus)) >>>> + continue; >>>> + >>>> + if (has_idle_core) { >>>> + i = select_idle_core(p, cpu, cpus, &idle_cpu); >>>> + if ((unsigned)i < nr_cpumask_bits) >>>> + return 1; >>>> + } else { >>>> + if (--nr <= 0) >>>> + return -1; >>>> + idle_cpu = __select_idle_cpu(cpu, p); >>>> + if ((unsigned)idle_cpu < nr_cpumask_bits) >>>> + return idle_cpu; >>>> + } >>>> + } >>>> + cpumask_andnot(cpus, cpus, sched_group_span(sg)); >>>> + } >>>> + } >>>> + >>>> for_each_cpu_wrap(cpu, cpus, target + 1) { >>>> if (has_idle_core) { >>>> i = select_idle_core(p, cpu, cpus, &idle_cpu); >>>> >>>> also work? Then we can avoid the extra sd_cluster per-cpu variable. >>>> >>> >>> I thought it will be fine since sg->flags is derived from the child domain. But practically it doesn't. >>> Tested on a 2P Skylake server with no clusters, add some debug messages to see how sg->flags appears: >>> >>> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c >>> index 69968ed9ffb9..5c443b74abf5 100644 >>> --- a/kernel/sched/topology.c >>> +++ b/kernel/sched/topology.c >>> @@ -90,8 +90,8 @@ static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level, >>> >>> cpumask_or(groupmask, groupmask, sched_group_span(group)); >>> >>> - printk(KERN_CONT " %d:{ span=%*pbl", >>> - group->sgc->id, >>> + printk(KERN_CONT " %d:{ cluster: %s span=%*pbl", >>> + group->sgc->id, group->flags & SD_CLUSTER ? "true" : "false", >>> cpumask_pr_args(sched_group_span(group))); >>> >>> if ((sd->flags & SD_OVERLAP) && >>> >>> Unfortunately the result doesn't match what I expected, the MC domain's sg->flags still marked >>> as cluster: >>> >>> [ 8.886099] CPU0 attaching sched-domain(s): >>> [ 8.889539] domain-0: span=0,40 level=SMT >>> [ 8.893538] groups: 0:{ cluster: false span=0 }, 40:{ cluster: false span=40 } >>> [ 8.897538] domain-1: span=0-19,40-59 level=MC >>> [ 8.901538] groups: 0:{ cluster: true span=0,40 cap=2048 }, 1:{ cluster: true span=1,41 cap=2048 }, 2:{ cluster: true span=2,42 cap=2048 }, 3:{ cluster: true span=3,43 cap=2048 }, 4:{ cluster: true span=4,44 cap=2048 }, 5:{ cluster: true span=5,45 cap=2048 }, 6:{ cluster: true span=6,46 cap=2048 }, 7:{ cluster: true span=7,47 cap=2048 }, 8:{ cluster: true span=8,48 cap=2048 }, 9:{ cluster: true span=9,49 cap=2048 }, 10:{ cluster: true span=10,50 cap=2048 }, 11:{ cluster: true span=11,51 cap=2048 }, 12:{ cluster: true span=12,52 cap=2048 }, 13:{ cluster: true span=13,53 cap=2048 }, 14:{ cluster: true span=14,54 cap=2048 }, 15:{ cluster: true span=15,55 cap=2048 }, 16:{ cluster: true span=16,56 cap=2048 }, 17:{ cluster: true span=17,57 cap=2048 }, 18:{ cluster: true span=18,58 cap=2048 }, 19:{ cluster: true span=19,59 cap=2048 } >>> [ 8.905538] domain-2: span=0-79 level=NUMA >>> [ 8.909538] groups: 0:{ cluster: false span=0-19,40-59 cap=40960 }, 20:{ cluster: false span=20-39,60-79 cap=40960 } >>> >>> I assume we didn't handle the sg->flags correctly on the domain degeneration. Simply checked the code seems >>> we've already make sg->flags = 0 on degeneration, maybe I need to check where's wrong. >>> >> >> Currently we only update the groups' flags to 0 for the final lowest domain in [1]. The upper >> domains' group won't be updated if degeneration happens. So we cannot use the suggested approach >> for cluster scanning and sd_cluster per-cpu variable is still needed. >> >> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/sched/topology.c?h=v6.4-rc4#n749 >> >> Thanks. >> >> > Is this an issue? Suppose sched domain A's parent domain > is B, B's parent sched domain is C. When B degenerates, C's child domain > pointer is adjusted to A. However, currently the code does not adjust C's > sched groups' flags. Should we adjust C's sched groups flags to be the same > as A to keep consistency? It depends on whether we're going to use it. currently only asym_smt_can_pull_tasks() uses it within the SMT so I think update the lowest domain's group flag works. For correctness all the domain group's flag should derives from its real child. I tried to solve this at group building but seems hard to do, at that time we don't know whether a domain is going to degenerate or not since the groups it not built. > > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > index 6198fa135176..fe3fd70f2313 100644 > --- a/kernel/sched/topology.c > +++ b/kernel/sched/topology.c > @@ -713,14 +713,13 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu) > > /* Remove the sched domains which do not contribute to scheduling. */ > for (tmp = sd; tmp; ) { > - struct sched_domain *parent = tmp->parent; > + struct sched_domain *parent = tmp->parent, *pparent; > if (!parent) > break; > > if (sd_parent_degenerate(tmp, parent)) { > - tmp->parent = parent->parent; > - if (parent->parent) > - parent->parent->child = tmp; > + pparent = parent->parent; > + tmp->parent = pparent; > /* > * Transfer SD_PREFER_SIBLING down in case of a > * degenerate parent; the spans match for this > @@ -728,6 +727,18 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu) > */ > if (parent->flags & SD_PREFER_SIBLING) > tmp->flags |= SD_PREFER_SIBLING; > + > + if (pparent) { > + struct sched_group *sg = pparent->groups; > + > + do { > + sg->flags = tmp->flags; May need to test on some heterogeous platforms. Does it always stand that child domain of CPU from remote group have the same flags with @tmp? > + sg = sg->next; > + } while (sg != pparent->groups); > + > + pparent->child = tmp; > + } > + > destroy_sched_domain(parent); > } else > tmp = tmp->parent; > The code you pasted at last of your mail is correct I think, not sure it doesn't appear here when reply... Thanks.