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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 D5691C1B0F2 for ; Wed, 20 Jun 2018 09:06:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9019520652 for ; Wed, 20 Jun 2018 09:06:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9019520652 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754818AbeFTJGp (ORCPT ); Wed, 20 Jun 2018 05:06:45 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:33932 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752308AbeFTJGi (ORCPT ); Wed, 20 Jun 2018 05:06:38 -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 7C5AD80D; Wed, 20 Jun 2018 02:06:38 -0700 (PDT) Received: from e105550-lin.cambridge.arm.com (e105550-lin.cambridge.arm.com [10.1.211.30]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 044A83F246; Wed, 20 Jun 2018 02:06:36 -0700 (PDT) From: Morten Rasmussen To: peterz@infradead.org, mingo@redhat.com Cc: valentin.schneider@arm.com, dietmar.eggemann@arm.com, vincent.guittot@linaro.org, gaku.inami.xh@renesas.com, linux-kernel@vger.kernel.org, Morten Rasmussen Subject: [PATCHv3 0/9] sched/fair: Migrate 'misfit' tasks on asymmetric capacity systems Date: Wed, 20 Jun 2018 10:05:40 +0100 Message-Id: <1529485549-5191-1-git-send-email-morten.rasmussen@arm.com> X-Mailer: git-send-email 2.7.4 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On asymmetric cpu capacity systems (e.g. Arm big.LITTLE) it is crucial for performance that cpu intensive tasks are aggressively migrated to high capacity cpus as soon as those become available. The capacity awareness tweaks already in the wake-up path can't handle this as such tasks might run or be runnable forever. If they happen to be placed on a low capacity cpu from the beginning they are stuck there forever while high capacity cpus may have become available in the meantime. To address this issue this patch set introduces a new "misfit" load-balancing scenario in periodic/nohz/newly idle balance which tweaks the load-balance conditions to ignore load per capacity in certain cases. Since misfit tasks are commonly running alone on a cpu, more aggressive active load-balancing is needed too. The fundamental idea of this patch set has been in Android kernels for a long time and is absolutely essential for consistent performance on asymmetric cpu capacity systems. The patches have been tested on: 1. Arm Juno (r0): 2+4 Cortex A57/A53 2. Hikey960: 4+4 Cortex A73/A53 Test case: Big cpus are always kept busy. Pin a shorter running sysbench tasks to big cpus, while creating a longer running set of unpinned sysbench tasks. REQUESTS=1000 BIGS="1 2" LITTLES="0 3 4 5" # Don't care about the score for those, just keep the bigs busy for i in $BIGS; do taskset -c $i sysbench --max-requests=$((REQUESTS / 4)) \ --test=cpu run &>/dev/null & done for i in $LITTLES; do sysbench --max-requests=$REQUESTS --test=cpu run \ | grep "total time:" & done wait Results: Single runs with completion time of each task Juno (tip) total time: 1.2608s total time: 1.2995s total time: 1.5954s total time: 1.7463s Juno (misfit) total time: 1.2575s total time: 1.3004s total time: 1.5860s total time: 1.5871s Hikey960 (tip) total time: 1.7431s total time: 2.2914s total time: 2.5976s total time: 1.7280s Hikey960 (misfit) total time: 1.7866s total time: 1.7513s total time: 1.6918s total time: 1.6965s 10 run summary (tracking longest running task for each run) Juno Hikey960 avg max avg max tip 1.7465 1.7469 2.5997 2.6131 misfit 1.6016 1.6192 1.8506 1.9666 Changelog: v3 - Fixed locking around static_key. - Changed group per-cpu capacity comparison to be based on max rather than min capacity. - Added patch to prevent occasional pointless high->low capacity migrations. - Changed type of group_misfit_task_load and misfit_task_load to unsigned long. - Changed fbq() to pick the cpu with highest misfit_task_load rather than breaking when the first is found. - Rebased against tip/sched/core. - v2 Tested-by: Gaku Inami v2 - Removed redudant condition in static_key enablement. - Fixed logic flaw in patch #2 reported by Yi Yao - Dropped patch #4 as although the patch seems to make sense no benefit has been proven. - Dropped root_domain->overload renaming - Changed type of root_domain->overload to int - Wrapped accesses of rq->rd->overload with READ/WRITE_ONCE - v1 Tested-by: Gaku Inami Chris Redpath (1): sched/fair: Don't move tasks to lower capacity cpus unless necessary Morten Rasmussen (4): sched: Add static_key for asymmetric cpu capacity optimizations sched/fair: Add group_misfit_task load-balance type sched: Add sched_group per-cpu max capacity sched/fair: Consider misfit tasks when load-balancing Valentin Schneider (4): sched/fair: Kick nohz balance if rq->misfit_task sched: Change root_domain->overload type to int sched: Wrap rq->rd->overload accesses with READ/WRITE_ONCE sched/fair: Set sd->overload when misfit kernel/sched/fair.c | 162 +++++++++++++++++++++++++++++++++++++++++------- kernel/sched/sched.h | 16 +++-- kernel/sched/topology.c | 20 ++++++ 3 files changed, 171 insertions(+), 27 deletions(-) -- 2.7.4