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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,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 10092C433DB for ; Fri, 19 Feb 2021 13:04:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BCC0164EBF for ; Fri, 19 Feb 2021 13:04:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230280AbhBSNEj (ORCPT ); Fri, 19 Feb 2021 08:04:39 -0500 Received: from foss.arm.com ([217.140.110.172]:35888 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230177AbhBSNDY (ORCPT ); Fri, 19 Feb 2021 08:03:24 -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 DB6EA13A1; Fri, 19 Feb 2021 05:02:37 -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 E16553F73B; Fri, 19 Feb 2021 05:02:35 -0800 (PST) From: Valentin Schneider To: linux-kernel@vger.kernel.org Cc: Qais Yousef , Peter Zijlstra , Ingo Molnar , Vincent Guittot , Dietmar Eggemann , Morten Rasmussen , Quentin Perret , Pavan Kondeti , Rik van Riel , Lingutla Chandrasekhar Subject: [PATCH v2 4/7] sched/fair: Introduce a CPU capacity comparison helper Date: Fri, 19 Feb 2021 13:00:00 +0000 Message-Id: <20210219130003.2890-5-valentin.schneider@arm.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20210219130003.2890-1-valentin.schneider@arm.com> References: <20210219130003.2890-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org During load-balance, groups classified as group_misfit_task are filtered out if they do not pass group_smaller_max_cpu_capacity(, ); which itself employs fits_capacity() to compare the sgc->max_capacity of both groups. Due to the underlying margin, fits_capacity(X, 1024) will return false for any X > 819. Tough luck, the capacity_orig's on e.g. the Pixel 4 are {261, 871, 1024}. If a CPU-bound task ends up on one of those "medium" CPUs, misfit migration will never intentionally upmigrate it to a CPU of higher capacity due to the aforementioned margin. One may argue the 20% margin of fits_capacity() is excessive in the advent of counter-enhanced load tracking (APERF/MPERF, AMUs), but one point here is that fits_capacity() is meant to compare a utilization value to a capacity value, whereas here it is being used to compare two capacity values. As CPU capacity and task utilization have different dynamics, a sensible approach here would be to add a new helper dedicated to comparing CPU capacities. Reviewed-by: Qais Yousef Signed-off-by: Valentin Schneider --- kernel/sched/fair.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 24119f9ad191..cc16d0e0b9fb 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -113,6 +113,13 @@ int __weak arch_asym_cpu_priority(int cpu) */ #define fits_capacity(cap, max) ((cap) * 1280 < (max) * 1024) +/* + * The margin used when comparing CPU capacities. + * is 'cap1' noticeably greater than 'cap2' + * + * (default: ~5%) + */ +#define capacity_greater(cap1, cap2) ((cap1) * 1024 > (cap2) * 1078) #endif #ifdef CONFIG_CFS_BANDWIDTH -- 2.27.0