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=-8.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_NEOMUTT 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 C4A3CC004C9 for ; Tue, 7 May 2019 15:57:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 97847205ED for ; Tue, 7 May 2019 15:57:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726608AbfEGP5j (ORCPT ); Tue, 7 May 2019 11:57:39 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:58270 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726438AbfEGP5j (ORCPT ); Tue, 7 May 2019 11:57:39 -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 8898A374; Tue, 7 May 2019 08:57:38 -0700 (PDT) Received: from queper01-lin (queper01-lin.cambridge.arm.com [10.1.195.48]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 08F583F5AF; Tue, 7 May 2019 08:57:35 -0700 (PDT) Date: Tue, 7 May 2019 16:57:34 +0100 From: Quentin Perret To: Luca Abeni Cc: linux-kernel@vger.kernel.org, Greg Kroah-Hartman , "Rafael J . Wysocki" , Ingo Molnar , Peter Zijlstra , Vincent Guittot , "Paul E . McKenney" , Joel Fernandes , Luc Van Oostenryck , Morten Rasmussen , Juri Lelli , Daniel Bristot de Oliveira , Patrick Bellasi , Tommaso Cucinotta Subject: Re: [RFC PATCH 6/6] sched/dl: Try not to select a too fast core Message-ID: <20190507155732.7ravrnld54rb6k5a@queper01-lin> References: <20190506044836.2914-1-luca.abeni@santannapisa.it> <20190506044836.2914-7-luca.abeni@santannapisa.it> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190506044836.2914-7-luca.abeni@santannapisa.it> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday 06 May 2019 at 06:48:36 (+0200), Luca Abeni wrote: > From: luca abeni > > When a task can fit on multiple CPU cores, try to select the slowest > core that is able to properly serve the task. This avoids useless > future migrations, leaving the "fast cores" idle for more heavyweight > tasks. But only if the _current_ capacity of big CPUs (at the current freq) is higher than the current capacity of the littles, is that right ? So we don't really have a guarantee to pack small tasks on little cores ... What is the rationale for looking at the current freq in dl_task_fit() ? Energy reasons ? If so, I'd argue you should look at the energy model to break the tie between CPU candidates ... ;) And in the mean time, you could just look at arch_scale_cpu_capacity() to check if a task fits ? > Signed-off-by: luca abeni > --- > kernel/sched/cpudeadline.c | 17 ++++++++++++----- > 1 file changed, 12 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c > index 2a4ac7b529b7..897ed71af515 100644 > --- a/kernel/sched/cpudeadline.c > +++ b/kernel/sched/cpudeadline.c > @@ -143,17 +143,24 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p, > struct cpumask *later_mask) > { > const struct sched_dl_entity *dl_se = &p->dl; > + struct cpumask tmp_mask; Hmm, these can get pretty big, so not sure about having one on the stack ... > > if (later_mask && > - cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) { > + cpumask_and(&tmp_mask, cp->free_cpus, &p->cpus_allowed)) { > int cpu, max_cpu = -1; > - u64 max_cap = 0; > + u64 max_cap = 0, min_cap = SCHED_CAPACITY_SCALE * SCHED_CAPACITY_SCALE; > > - for_each_cpu(cpu, later_mask) { > + cpumask_clear(later_mask); > + for_each_cpu(cpu, &tmp_mask) { > u64 cap; > > - if (!dl_task_fit(&p->dl, cpu, &cap)) > - cpumask_clear_cpu(cpu, later_mask); > + if (dl_task_fit(&p->dl, cpu, &cap) && (cap <= min_cap)) { > + if (cap < min_cap) { > + min_cap = cap; > + cpumask_clear(later_mask); > + } > + cpumask_set_cpu(cpu, later_mask); > + } > > if (cap > max_cap) { > max_cap = cap; > -- > 2.20.1 > Thanks, Quentin