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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 A49D6C433B4 for ; Mon, 19 Apr 2021 17:13:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 70C6960FEA for ; Mon, 19 Apr 2021 17:13:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239868AbhDSROC convert rfc822-to-8bit (ORCPT ); Mon, 19 Apr 2021 13:14:02 -0400 Received: from foss.arm.com ([217.140.110.172]:46950 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239824AbhDSRNz (ORCPT ); Mon, 19 Apr 2021 13:13:55 -0400 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 8349014BF; Mon, 19 Apr 2021 10:13:25 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 155833F7D7; Mon, 19 Apr 2021 10:13:23 -0700 (PDT) From: Valentin Schneider To: Vincent Guittot Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Dietmar Eggemann , Morten Rasmussen , Qais Yousef , Quentin Perret , Pavan Kondeti , Rik van Riel , Lingutla Chandrasekhar Subject: Re: [PATCH 2/2] sched/fair: Relax task_hot() for misfit tasks In-Reply-To: <20210416135113.GA16445@vingu-book> References: <20210415175846.494385-1-valentin.schneider@arm.com> <20210415175846.494385-3-valentin.schneider@arm.com> <20210416135113.GA16445@vingu-book> Date: Mon, 19 Apr 2021 18:13:21 +0100 Message-ID: <87blaakxji.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16/04/21 15:51, Vincent Guittot wrote: > Le jeudi 15 avril 2021 � 18:58:46 (+0100), Valentin Schneider a �crit : >> + >> +/* >> + * What does migrating this task do to our capacity-aware scheduling criterion? >> + * >> + * Returns 1, if the task needs more capacity than the dst CPU can provide. >> + * Returns 0, if the task needs the extra capacity provided by the dst CPU >> + * Returns -1, if the task isn't impacted by the migration wrt capacity. >> + */ >> +static int migrate_degrades_capacity(struct task_struct *p, struct lb_env *env) >> +{ >> + if (!(env->sd->flags & SD_ASYM_CPUCAPACITY)) >> + return -1; >> + >> + if (!task_fits_capacity(p, capacity_of(env->src_cpu))) { >> + if (cpu_capacity_greater(env->dst_cpu, env->src_cpu)) >> + return 0; >> + else if (cpu_capacity_greater(env->src_cpu, env->dst_cpu)) >> + return 1; >> + else >> + return -1; >> + } > > Being there means that task fits src_cpu capacity so why testing p against dst_cpu ? > Because if p fits on src_cpu, we don't want to move it to a dst_cpu on which it *doesn't* fit. >> + >> + return task_fits_capacity(p, capacity_of(env->dst_cpu)) ? -1 : 1; >> +} > > I prefer the below which easier to read because the same var is use everywhere and you can remove cpu_capacity_greater. > > static int migrate_degrades_capacity(struct task_struct *p, struct lb_env *env) > { > unsigned long src_capacity, dst_capacity; > > if (!(env->sd->flags & SD_ASYM_CPUCAPACITY)) > return -1; > > src_capacity = capacity_of(env->src_cpu); > dst_capacity = capacity_of(env->dst_cpu); > > if (!task_fits_capacity(p, src_capacity)) { > if (capacity_greater(dst_capacity, src_capacity)) > return 0; > else if (capacity_greater(src_capacity, dst_capacity)) > return 1; > else > return -1; > } > > return task_fits_capacity(p, dst_capacity) ? -1 : 1; > } > I'll take it, thanks! > >> + >> #ifdef CONFIG_NUMA_BALANCING >> /* >> * Returns 1, if task migration degrades locality >> @@ -7672,6 +7698,15 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) >> if (tsk_cache_hot == -1) >> tsk_cache_hot = task_hot(p, env); >> >> + /* >> + * On a (sane) asymmetric CPU capacity system, the increase in compute >> + * capacity should offset any potential performance hit caused by a >> + * migration. >> + */ >> + if ((env->dst_grp_type == group_has_spare) && > > Shouldn't it be env->src_grp_type == group_misfit_task to only care of misfit task case as > stated in $subject > Previously this was env->idle != CPU_NOT_IDLE, but I figured dst_grp_type could give us a better picture. Staring at this some more, this isn't so true when the group size goes up - there's no guarantees the dst_cpu is the one that has spare cycles, and the other CPUs might not be able to grant the capacity uplift dst_cpu can. As for not using src_grp_type == group_misfit_task, this is pretty much the same as [1]. CPU-bound (misfit) task + some other task on the same rq implies group_overloaded classification when balancing at MC level (no SMT, so one group per CPU). [1]: http://lore.kernel.org/r/jhjblcuv2mo.mognet@arm.com