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=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham 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 2CDB7C10F0E for ; Tue, 9 Apr 2019 17:36:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F2C0120857 for ; Tue, 9 Apr 2019 17:36:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726666AbfDIRg6 (ORCPT ); Tue, 9 Apr 2019 13:36:58 -0400 Received: from foss.arm.com ([217.140.101.70]:42152 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726460AbfDIRgz (ORCPT ); Tue, 9 Apr 2019 13:36:55 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 287D41682; Tue, 9 Apr 2019 10:36:55 -0700 (PDT) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id C654F3F59C; Tue, 9 Apr 2019 10:36:53 -0700 (PDT) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: mingo@redhat.com, peterz@infradead.org, Dietmar.Eggemann@arm.com, morten.rasmussen@arm.com, qais.yousef@arm.com Subject: [PATCH 1/2] sched/topology: build_sched_groups: Skip duplicate group rewrites Date: Tue, 9 Apr 2019 18:35:45 +0100 Message-Id: <20190409173546.4747-2-valentin.schneider@arm.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190409173546.4747-1-valentin.schneider@arm.com> References: <20190409173546.4747-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org While staring at build_sched_domains(), I realized that get_group() does several duplicate (thus useless) writes. If you take the Arm Juno r0 (LITTLEs = [0, 3, 4, 5], bigs = [1, 2]), the sched_group build flow would look like this: ('MC[cpu]->sg' means 'per_cpu_ptr(&tl->data->sg, cpu)' with 'tl == MC') build_sched_groups(MC[CPU0]->sd, CPU0) get_group(0) -> MC[CPU0]->sg get_group(3) -> MC[CPU3]->sg get_group(4) -> MC[CPU4]->sg get_group(5) -> MC[CPU5]->sg build_sched_groups(DIE[CPU0]->sd, CPU0) get_group(0) -> DIE[CPU0]->sg get_group(1) -> DIE[CPU1]->sg <-----------------+ | build_sched_groups(MC[CPU1]->sd, CPU1) | get_group(1) -> MC[CPU1]->sg | get_group(2) -> MC[CPU2]->sg | | build_sched_groups(DIE[CPU1]->sd, CPU1) ^ get_group(1) -> DIE[CPU1]->sg } We've set up these two up here! get_group(3) -> DIE[CPU0]->sg } >From this point on, we will only use sched_groups that have been previously visited & initialized. The only new operation will be which group pointer we affect to sd->groups. On the Juno r0 we get 32 get_group() calls, every single one of them writing to a sched_group->cpumask. However, all of the data structures we need are set up after 8 visits (see above). Return early from get_group() if we've already visited (and thus initialized) the sched_group we're looking at. Overlapping domains are not affected as they do not use build_sched_groups(). Tested on a Juno and a 2 * (Xeon E5-2690) system. Signed-off-by: Valentin Schneider --- FWIW I initially checked the refs for both sg && sg->sgc, but figured if they weren't both 0 or > 1 then something must have gone wrong, so I threw in a WARN_ON(). --- kernel/sched/topology.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 64bec54ded3e..6c0b7326f66e 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1059,6 +1059,7 @@ static struct sched_group *get_group(int cpu, struct sd_data *sdd) struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu); struct sched_domain *child = sd->child; struct sched_group *sg; + bool already_visited; if (child) cpu = cpumask_first(sched_domain_span(child)); @@ -1066,9 +1067,14 @@ static struct sched_group *get_group(int cpu, struct sd_data *sdd) sg = *per_cpu_ptr(sdd->sg, cpu); sg->sgc = *per_cpu_ptr(sdd->sgc, cpu); - /* For claim_allocations: */ - atomic_inc(&sg->ref); - atomic_inc(&sg->sgc->ref); + /* Increase refcounts for claim_allocations: */ + already_visited = atomic_inc_return(&sg->ref) > 1; + /* sgc visits should follow a similar trend as sg */ + WARN_ON(already_visited != (atomic_inc_return(&sg->sgc->ref) > 1)); + + /* If we have already visited that group, it's already initialized. */ + if (already_visited) + return sg; if (child) { cpumask_copy(sched_group_span(sg), sched_domain_span(child)); -- 2.20.1