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=-11.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, 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 2DB49C433DB for ; Fri, 19 Feb 2021 13:03:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CA1DA64E15 for ; Fri, 19 Feb 2021 13:03:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230144AbhBSNDV (ORCPT ); Fri, 19 Feb 2021 08:03:21 -0500 Received: from foss.arm.com ([217.140.110.172]:35824 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229868AbhBSNDQ (ORCPT ); Fri, 19 Feb 2021 08:03:16 -0500 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 5B81C1FB; Fri, 19 Feb 2021 05:02:30 -0800 (PST) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id BEA863F73B; Fri, 19 Feb 2021 05:02:28 -0800 (PST) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Morten Rasmussen , Qais Yousef , Quentin Perret , Pavan Kondeti , Rik van Riel , Lingutla Chandrasekhar Subject: [PATCH v2 0/7] sched/fair: misfit task load-balance tweaks Date: Fri, 19 Feb 2021 12:59:56 +0000 Message-Id: <20210219130003.2890-1-valentin.schneider@arm.com> X-Mailer: git-send-email 2.27.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi folks, Here is this year's series of misfit changes. On the menu: o Patch 1 prevents pcpu kworkers from causing group_imbalanced o Patch 2 is an independent active balance cleanup o Patch 3 adds some more sched_asym_cpucapacity static branches o Patch 4 introduces yet another margin for capacity to capacity comparisons o Patches 5-6 build on top of patch 4 and change capacity comparisons throughout misfit load balancing o Patch 7 aligns running and non-running misfit task cache hotness considerations IMO the somewhat controversial bit is patch 4, because it attempts to solve margin issues by... Adding another margin. This does solve issues on existing platforms (e.g. Pixel4), but we'll be back to square one the day some "clever" folks spin a platform with two different CPU capacities less than 5% apart. This is based on top of today's tip/sched/core at: c5e6fc08feb2 ("sched,x86: Allow !PREEMPT_DYNAMIC") Testing ======= I ran my usual [1] misfit tests on o TC2 o Juno o HiKey960 o Dragonboard845C o RB5 RB5 has a similar topology to Pixel4 and highlights the problem of having two different CPU capacity values above 819 (in this case 871 and 1024): without these patches, CPU hogs (i.e. misfit tasks) running on the "medium" CPUs will never be upmigrated to a "big" via misfit balance. Revisions ========= v1 -> v2 -------- o Collected Reviewed-by o Minor comment and code cleanups o Consolidated static key vs SD flag explanation (Dietmar) Note to Vincent: I didn't measure the impact of adding said static key to load_balance(); I do however believe it is a low hanging fruit. The wrapper keeps things neat and tidy, and is also helpful for documenting the intricacies of the static key status vs the presence of the SD flag in a CPU's sched_domain hierarchy. o Removed v1 patch 4 - root_domain.max_cpu_capacity is absolutely not what I had convinced myself it was. o Squashed capacity margin usage with removal of group_smaller_{min, max}_capacity() (Vincent) o Replaced v1 patch 7 with Lingutla's can_migrate_task() patch [2] o Rewrote task_hot() modification changelog Links ===== [1]: https://lisa-linux-integrated-system-analysis.readthedocs.io/en/master/kernel_tests.html#lisa.tests.scheduler.misfit.StaggeredFinishes [2]: http://lore.kernel.org/r/20210217120854.1280-1-clingutla@codeaurora.org Cheers, Valentin Lingutla Chandrasekhar (1): sched/fair: Ignore percpu threads for imbalance pulls Valentin Schneider (6): sched/fair: Clean up active balance nr_balance_failed trickery sched/fair: Add more sched_asym_cpucapacity static branch checks sched/fair: Introduce a CPU capacity comparison helper sched/fair: Employ capacity_greater() throughout load_balance() sched/fair: Filter out locally-unsolvable misfit imbalances sched/fair: Relax task_hot() for misfit tasks kernel/sched/fair.c | 128 ++++++++++++++++++++++++------------------- kernel/sched/sched.h | 33 +++++++++++ 2 files changed, 105 insertions(+), 56 deletions(-) -- 2.27.0