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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 74C49C4321A for ; Tue, 2 Mar 2021 10:11:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F62260240 for ; Tue, 2 Mar 2021 10:11:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1379134AbhCBKFT (ORCPT ); Tue, 2 Mar 2021 05:05:19 -0500 Received: from foss.arm.com ([217.140.110.172]:47644 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1577798AbhCBJyF (ORCPT ); Tue, 2 Mar 2021 04:54:05 -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 3430EED1; Tue, 2 Mar 2021 01:53:18 -0800 (PST) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1A3EF3F70D; Tue, 2 Mar 2021 01:53:15 -0800 (PST) Subject: Re: [PATCH] sched/fair: Prefer idle CPU to cache affinity To: Srikar Dronamraju , Ingo Molnar , Peter Zijlstra Cc: LKML , Mel Gorman , Rik van Riel , Thomas Gleixner , Valentin Schneider , Vincent Guittot , Michael Ellerman , Michael Neuling , Gautham R Shenoy , Parth Shah References: <20210226164029.122432-1-srikar@linux.vnet.ibm.com> From: Dietmar Eggemann Message-ID: <19bfd781-05f7-b220-d8a2-fde8ea2d9959@arm.com> Date: Tue, 2 Mar 2021 10:53:06 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210226164029.122432-1-srikar@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/02/2021 17:40, Srikar Dronamraju wrote: [...] > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 8a8bd7b13634..d49bfcdc4a19 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -5869,6 +5869,36 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p, > return this_eff_load < prev_eff_load ? this_cpu : nr_cpumask_bits; > } > > +static int prefer_idler_llc(int this_cpu, int prev_cpu, int sync) > +{ > + struct sched_domain_shared *tsds, *psds; > + int pnr_busy, pllc_size, tnr_busy, tllc_size, diff; > + > + tsds = rcu_dereference(per_cpu(sd_llc_shared, this_cpu)); > + tnr_busy = atomic_read(&tsds->nr_busy_cpus); > + tllc_size = per_cpu(sd_llc_size, this_cpu); > + > + psds = rcu_dereference(per_cpu(sd_llc_shared, prev_cpu)); > + pnr_busy = atomic_read(&psds->nr_busy_cpus); > + pllc_size = per_cpu(sd_llc_size, prev_cpu); > + > + /* No need to compare, if both LLCs are fully loaded */ > + if (pnr_busy == pllc_size && tnr_busy == pllc_size) ^ shouldn't this be tllc_size ? > + return nr_cpumask_bits; > + > + if (sched_feat(WA_WAKER) && tnr_busy < tllc_size) > + return this_cpu; > + > + /* For better wakeup latency, prefer idler LLC to cache affinity */ > + diff = tnr_busy * pllc_size - sync - pnr_busy * tllc_size; > + if (!diff) > + return nr_cpumask_bits; > + if (diff < 0) > + return this_cpu; > + > + return prev_cpu; > +} > +