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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 214FEC34022 for ; Mon, 17 Feb 2020 19:09:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 044502070B for ; Mon, 17 Feb 2020 19:09:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729529AbgBQTJ1 (ORCPT ); Mon, 17 Feb 2020 14:09:27 -0500 Received: from foss.arm.com ([217.140.110.172]:41148 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728448AbgBQTJ1 (ORCPT ); Mon, 17 Feb 2020 14:09:27 -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 021971FB; Mon, 17 Feb 2020 11:09:27 -0800 (PST) Received: from [192.168.0.7] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 75EB93F68F; Mon, 17 Feb 2020 11:09:25 -0800 (PST) Subject: Re: [PATCH 1/3] sched/rt: cpupri_find: implement fallback mechanism for !fit case To: Qais Yousef , Ingo Molnar , Peter Zijlstra , Steven Rostedt , Pavan Kondeti Cc: Juri Lelli , Vincent Guittot , Ben Segall , Mel Gorman , linux-kernel@vger.kernel.org References: <20200214163949.27850-1-qais.yousef@arm.com> <20200214163949.27850-2-qais.yousef@arm.com> From: Dietmar Eggemann Message-ID: Date: Mon, 17 Feb 2020 20:09:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200214163949.27850-2-qais.yousef@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14/02/2020 17:39, Qais Yousef wrote: [...] > /** > * cpupri_find - find the best (lowest-pri) CPU in the system > * @cp: The cpupri context > @@ -62,80 +115,72 @@ int cpupri_find(struct cpupri *cp, struct task_struct *p, > struct cpumask *lowest_mask, > bool (*fitness_fn)(struct task_struct *p, int cpu)) > { > - int idx = 0; > int task_pri = convert_prio(p->prio); > + int best_unfit_idx = -1; > + int idx = 0, cpu; > > BUG_ON(task_pri >= CPUPRI_NR_PRIORITIES); > > for (idx = 0; idx < task_pri; idx++) { > - struct cpupri_vec *vec = &cp->pri_to_cpu[idx]; > - int skip = 0; > > - if (!atomic_read(&(vec)->count)) > - skip = 1; > - /* > - * When looking at the vector, we need to read the counter, > - * do a memory barrier, then read the mask. > - * > - * Note: This is still all racey, but we can deal with it. > - * Ideally, we only want to look at masks that are set. > - * > - * If a mask is not set, then the only thing wrong is that we > - * did a little more work than necessary. > - * > - * If we read a zero count but the mask is set, because of the > - * memory barriers, that can only happen when the highest prio > - * task for a run queue has left the run queue, in which case, > - * it will be followed by a pull. If the task we are processing > - * fails to find a proper place to go, that pull request will > - * pull this task if the run queue is running at a lower > - * priority. > - */ > - smp_rmb(); > - > - /* Need to do the rmb for every iteration */ > - if (skip) > - continue; > - > - if (cpumask_any_and(p->cpus_ptr, vec->mask) >= nr_cpu_ids) > + if (!__cpupri_find(cp, p, lowest_mask, idx)) > continue; > > - if (lowest_mask) { > - int cpu; Shouldn't we add an extra condition here? + if (!static_branch_unlikely(&sched_asym_cpucapacity)) + return 1; + Otherwise non-heterogeneous systems have to got through this for_each_cpu(cpu, lowest_mask) further below for no good reason. > + if (!lowest_mask || !fitness_fn) > + return 1; > > - cpumask_and(lowest_mask, p->cpus_ptr, vec->mask); > + /* Ensure the capacity of the CPUs fit the task */ > + for_each_cpu(cpu, lowest_mask) { > + if (!fitness_fn(p, cpu)) > + cpumask_clear_cpu(cpu, lowest_mask); > + } [...]