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[23.128.96.18]) by mx.google.com with ESMTP id i26si329911ion.51.2021.05.26.06.08.53; Wed, 26 May 2021 06:09:09 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=arm.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233720AbhEZMRb (ORCPT + 99 others); Wed, 26 May 2021 08:17:31 -0400 Received: from foss.arm.com ([217.140.110.172]:43706 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232546AbhEZMRa (ORCPT ); Wed, 26 May 2021 08:17:30 -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 2FEDB1516; Wed, 26 May 2021 05:15:59 -0700 (PDT) Received: from e120325.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AB1743F73B; Wed, 26 May 2021 05:15:57 -0700 (PDT) Date: Wed, 26 May 2021 13:15:49 +0100 From: Beata Michalska To: Dietmar Eggemann Cc: Valentin Schneider , linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, corbet@lwn.net, rdunlap@infradead.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry detection Message-ID: <20210526121546.GA13262@e120325.cambridge.arm.com> References: <20210524101617.8965-1-beata.michalska@arm.com> <20210524101617.8965-3-beata.michalska@arm.com> <87fsyc6mfz.mognet@arm.com> <20210524225508.GA14880@e120325.cambridge.arm.com> <87a6oj6sxo.mognet@arm.com> <20210525102945.GA24210@e120325.cambridge.arm.com> <98ad8837-b9b8-ff50-5a91-8d5951ee757c@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <98ad8837-b9b8-ff50-5a91-8d5951ee757c@arm.com> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 26, 2021 at 11:52:25AM +0200, Dietmar Eggemann wrote: > On 25/05/2021 12:29, Beata Michalska wrote: > > On Tue, May 25, 2021 at 10:53:07AM +0100, Valentin Schneider wrote: > >> On 24/05/21 23:55, Beata Michalska wrote: > >>> On Mon, May 24, 2021 at 07:01:04PM +0100, Valentin Schneider wrote: > >>>> On 24/05/21 11:16, Beata Michalska wrote: > > [...] > > >>>>> +static inline int > >>>>> +asym_cpu_capacity_classify(struct sched_domain *sd, > >>>>> + const struct cpumask *cpu_map) > >>>>> +{ > >>>>> + int sd_asym_flags = SD_ASYM_CPUCAPACITY | SD_ASYM_CPUCAPACITY_FULL; > >>>>> + struct asym_cap_data *entry; > >>>>> + int asym_cap_count = 0; > >>>>> + > >>>>> + if (list_is_singular(&asym_cap_list)) > >>>>> + goto leave; > >>>>> + > >>>>> + list_for_each_entry(entry, &asym_cap_list, link) { > >>>>> + if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask)) { > >>>>> + ++asym_cap_count; > >>>>> + } else { > >>>>> + /* > >>>>> + * CPUs with given capacity might be offline > >>>>> + * so make sure this is not the case > >>>>> + */ > >>>>> + if (cpumask_intersects(entry->cpu_mask, cpu_map)) { > >>>>> + sd_asym_flags &= ~SD_ASYM_CPUCAPACITY_FULL; > >>>>> + if (asym_cap_count > 1) > >>>>> + break; > >>>>> + } > >>>> > >>>> Readability nit: That could be made into an else if (). > >>> It could but then this way the -comment- gets more exposed. > >>> But that might be my personal perception so I can change that. > >> > >> As always those are quite subjective! Methink something like this would > >> still draw attention to the offline case: > >> > >> /* > >> * Count how many unique capacities this domain covers. If a > >> * capacity isn't covered, we need to check if any CPU with > >> * that capacity is actually online, otherwise it can be > >> * ignored. > >> */ > >> if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask)) { > >> ++asym_cap_count; > >> } else if (cpumask_intersects(entry->cpu_mask, cpu_map)) { > >> sd_asym_flags &= ~SD_ASYM_CPUCAPACITY_FULL; > >> if (asym_cap_count > 1) > >> break; > >> } > > Noted. > > Will wait for some more comments before sending out 'polished' version. > > For me asym_cpu_capacity_classify() is pretty hard to digest ;-) But I > wasn't able to break it. It also performs correctly on (non-existing SMT) > layer (with sd span eq. single CPU). > > Something like this (separating asym_cap_list iteration and flags > construction would be easier for me. But like already said here, > it's subjective. > I left the two optimizations (list_is_singular(), break on asym_cap_count > > 1) out for now. asym_cap_list shouldn't have > 4 entries (;-)). > > static inline int > asym_cpu_capacity_classify(struct sched_domain *sd, > const struct cpumask *cpu_map) > { > int sd_span_match = 0, cpu_map_match = 0, flags = 0; > struct asym_cap_data *entry; > > list_for_each_entry(entry, &asym_cap_list, link) { > if (cpumask_intersects(sched_domain_span(sd), entry->cpu_mask)) > ++sd_span_match; > else if (cpumask_intersects(cpu_map, entry->cpu_mask)) > ++cpu_map_match; > } > > WARN_ON_ONCE(!sd_span_match); > > if (sd_span_match > 1) { > flags |= SD_ASYM_CPUCAPACITY; > if (!cpu_map_match) > flags |= SD_ASYM_CPUCAPACITY_FULL; > } > > return flags; > } So I planned to drop the list_is_singular check as it is needless really. Otherwise, I am not really convinced by the suggestion. I could add comments around current version to make it more ..... 'digestible' but I'd rather stay with it as it seems more compact to me (subjective). > > BTW, how would this mechanism behave on a system with SMT and asymmetric CPU > capacity? Something EAS wouldn't allow but I guess asym_cap_list will be > constructed and the SD_ASYM_CPUCAPACITY_XXX flags will be set? Yes, the list would get created and flags set. I do not think there is a difference with current approach (?). So EAS would be disabled (it only cares about SD_ASYM_CPUCAPACITY_FULL flag) but the misift might still kick in. --- BR B.