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=-15.2 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_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 25FACC4361B for ; Mon, 14 Dec 2020 14:01:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D2A0E22B40 for ; Mon, 14 Dec 2020 14:01:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2408071AbgLNOB1 (ORCPT ); Mon, 14 Dec 2020 09:01:27 -0500 Received: from foss.arm.com ([217.140.110.172]:47812 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725811AbgLNOB0 (ORCPT ); Mon, 14 Dec 2020 09:01:26 -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 AEFEC30E; Mon, 14 Dec 2020 06:00:40 -0800 (PST) Received: from localhost (unknown [10.1.198.32]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3DAAF3F66E; Mon, 14 Dec 2020 06:00:40 -0800 (PST) Date: Mon, 14 Dec 2020 14:00:38 +0000 From: Ionela Voinescu To: Viresh Kumar Cc: Catalin Marinas , Will Deacon , Vincent Guittot , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2 2/2] arm64: topology: Reorder init_amu_fie() a bit Message-ID: <20201214140038.GB15405@arm.com> References: <5f85c2ddf7aa094d7d2ebebe8426f84fad0a99b7.1607617625.git.viresh.kumar@linaro.org> <202f775d57bd143602f9100ba3d9619d15d43409.1607617625.git.viresh.kumar@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202f775d57bd143602f9100ba3d9619d15d43409.1607617625.git.viresh.kumar@linaro.org> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hey, On Thursday 10 Dec 2020 at 21:59:23 (+0530), Viresh Kumar wrote: > This patch does a couple of optimizations in init_amu_fie(), like early > exits from paths where we don't need to continue any further, moving the > calls to topology_scale_freq_invariant() just when we need > them, instead of at the top of the routine, and avoiding calling it for > the third time. > > Signed-off-by: Viresh Kumar > --- > V2: > - The enable/disable dance is actually required, just made a bunch of > other optimizations to make it look better. > > arch/arm64/kernel/topology.c | 22 ++++++++++++++-------- > 1 file changed, 14 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c > index ebadc73449f9..1ebdb667f0d1 100644 > --- a/arch/arm64/kernel/topology.c > +++ b/arch/arm64/kernel/topology.c > @@ -221,7 +221,7 @@ static DEFINE_STATIC_KEY_FALSE(amu_fie_key); > > static int __init init_amu_fie(void) > { > - bool invariance_status = topology_scale_freq_invariant(); > + bool prev, now; Nit: can you move this below valid_cpus? It makes the section nicer if they are in decreasing order of line length. > cpumask_var_t valid_cpus; > int ret = 0; > int cpu; > @@ -249,18 +249,24 @@ static int __init init_amu_fie(void) > if (cpumask_equal(valid_cpus, cpu_present_mask)) > cpumask_copy(amu_fie_cpus, cpu_present_mask); > > - if (!cpumask_empty(amu_fie_cpus)) { > - pr_info("CPUs[%*pbl]: counters will be used for FIE.", > - cpumask_pr_args(amu_fie_cpus)); > - static_branch_enable(&amu_fie_key); > - } > + if (cpumask_empty(amu_fie_cpus)) > + goto free_valid_mask; > + > + prev = topology_scale_freq_invariant(); > + static_branch_enable(&amu_fie_key); I think there could be a potential problem here (it would be unlikely but why not fix it :) ). It was in the code before your changes. When we enable amu_fie_key here, topology_scale_freq_tick() could be called for AMU CPUs, which will compute and set a scale factor. Later on, if we happen to find the system not invariant, we disable counter based invariance, but a scale factor might have been set already for a CPU, which would and should have returned 1024 otherwise (the initialisation value of freq_scale). Therefore, while here, you could instead do the following: cpufreq_inv = cpufreq_supports_freq_invariance(); if (!cpufreq_inv && !cpumask_subset(cpu_online_mask, amu_fie_cpus)) goto free_valid_mask; static_branch_enable(&amu_fie_key); pr_info(..); if (!cpufreq_inv) rebuild_sched_domains_energy(); What do you think? I can submit this separately, if you don't want the hassle. Thanks, Ionela. > + now = topology_scale_freq_invariant(); > > /* > * If the system is not fully invariant after AMU init, disable > * partial use of counters for frequency invariance. > */ > - if (!topology_scale_freq_invariant()) > + if (!now) { > static_branch_disable(&amu_fie_key); > + goto free_valid_mask; > + } > + > + pr_info("CPUs[%*pbl]: counters will be used for FIE.", > + cpumask_pr_args(amu_fie_cpus)); > > /* > * Task scheduler behavior depends on frequency invariance support, > @@ -268,7 +274,7 @@ static int __init init_amu_fie(void) > * a result of counter initialisation and use, retrigger the build of > * scheduling domains to ensure the information is propagated properly. > */ > - if (invariance_status != topology_scale_freq_invariant()) > + if (prev != now) > rebuild_sched_domains_energy(); > > free_valid_mask: > -- > 2.25.0.rc1.19.g042ed3e048af >