From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965804AbdEOO4Y (ORCPT ); Mon, 15 May 2017 10:56:24 -0400 Received: from foss.arm.com ([217.140.101.70]:54222 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934147AbdEOO4X (ORCPT ); Mon, 15 May 2017 10:56:23 -0400 Subject: Re: [RFC 1/2] sched/fair: Fix load_balance() affinity redo path To: Jeffrey Hugo , Peter Zijlstra References: <1494608498-4538-1-git-send-email-jhugo@codeaurora.org> <1494608498-4538-2-git-send-email-jhugo@codeaurora.org> <20170512204754.GK4626@worktop.programming.kicks-ass.net> <9580a899-0fdb-7c14-c6e5-397f7d52bcf2@codeaurora.org> Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Austin Christ , Tyler Baicar From: Dietmar Eggemann Message-ID: <9b97fa6f-2b3d-3e10-fd55-208ef47f3e2a@arm.com> Date: Mon, 15 May 2017 15:56:20 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <9580a899-0fdb-7c14-c6e5-397f7d52bcf2@codeaurora.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/05/17 21:57, Jeffrey Hugo wrote: > On 5/12/2017 2:47 PM, Peter Zijlstra wrote: >> On Fri, May 12, 2017 at 11:01:37AM -0600, Jeffrey Hugo wrote: >>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >>> index d711093..8f783ba 100644 >>> --- a/kernel/sched/fair.c >>> +++ b/kernel/sched/fair.c >>> @@ -8219,8 +8219,19 @@ static int load_balance(int this_cpu, struct >>> rq *this_rq, >>> /* All tasks on this runqueue were pinned by CPU affinity */ >>> if (unlikely(env.flags & LBF_ALL_PINNED)) { >>> + struct cpumask tmp; >> >> You cannot have cpumask's on stack. > > Well, we need a temp variable to store the intermediate values since the > cpumask_* operations are somewhat limited, and require a "storage" > parameter. > > Do you have any suggestions to meet all of these requirements? What about we use env.dst_grpmask and check if cpus is an improper subset of env.dst_grpmask? In this case we have to get rid of setting env.dst_grpmask = NULL in case of CPU_NEWLY_IDLE which is IMHO not an issue since it's idle is passed via env into can_migrate_task(). And cpus has to be and'ed with sched_domain_span(env.sd). I'm not sure if this will work with 'not fully connected NUMA' (SD_OVERLAP) though ... diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a903276fcb62..2ede4c1c9db8 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6737,10 +6737,10 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) * our sched_group. We may want to revisit it if we couldn't * meet load balance goals by pulling other tasks on src_cpu. * - * Also avoid computing new_dst_cpu if we have already computed - * one in current iteration. + * Avoid computing new_dst_cpu for NEWLY_IDLE or if we have + * already computed one in current iteration. */ - if (!env->dst_grpmask || (env->flags & LBF_DST_PINNED)) + if (env->idle == CPU_NEWLY_IDLE || (env->flags & LBF_DST_PINNED)) return 0; /* Prevent to re-select dst_cpu via env's cpus */ @@ -8091,14 +8091,7 @@ static int load_balance(int this_cpu, struct rq *this_rq, .tasks = LIST_HEAD_INIT(env.tasks), }; - /* - * For NEWLY_IDLE load_balancing, we don't need to consider - * other cpus in our group - */ - if (idle == CPU_NEWLY_IDLE) - env.dst_grpmask = NULL; - - cpumask_copy(cpus, cpu_active_mask); + cpumask_and(cpus, cpu_active_mask, sched_domain_span(env.sd)); schedstat_inc(sd->lb_count[idle]); @@ -8220,7 +8213,7 @@ static int load_balance(int this_cpu, struct rq *this_rq, /* All tasks on this runqueue were pinned by CPU affinity */ if (unlikely(env.flags & LBF_ALL_PINNED)) { cpumask_clear_cpu(cpu_of(busiest), cpus); - if (!cpumask_empty(cpus)) { + if (!cpumask_subset(cpus, env.dst_grpmask)) { env.loop = 0; env.loop_break = sched_nr_migrate_break; goto redo;