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[23.128.96.18]) by mx.google.com with ESMTP id cb25si312459ejb.709.2021.06.02.10.19.19; Wed, 02 Jun 2021 10:19:42 -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 S229710AbhFBRTE (ORCPT + 99 others); Wed, 2 Jun 2021 13:19:04 -0400 Received: from foss.arm.com ([217.140.110.172]:50422 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229667AbhFBRTD (ORCPT ); Wed, 2 Jun 2021 13:19:03 -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 8E75F11FB; Wed, 2 Jun 2021 10:17:19 -0700 (PDT) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 066933F719; Wed, 2 Jun 2021 10:17:17 -0700 (PDT) Subject: Re: [PATCH v5 2/3] sched/topology: Rework CPU capacity asymmetry detection To: Beata Michalska 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 References: <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> <20210526121546.GA13262@e120325.cambridge.arm.com> <20210526125133.GB13262@e120325.cambridge.arm.com> <20210526214004.GA1712@e120325.cambridge.arm.com> <14593ba7-eed9-f035-724c-5cadbb859adc@arm.com> <20210527170729.GA20994@e120325.cambridge.arm.com> From: Dietmar Eggemann Message-ID: <4f43a9a8-b64e-bb47-b3c1-f51165f40249@arm.com> Date: Wed, 2 Jun 2021 19:17:12 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210527170729.GA20994@e120325.cambridge.arm.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 27/05/2021 19:07, Beata Michalska wrote: > On Thu, May 27, 2021 at 05:08:42PM +0200, Dietmar Eggemann wrote: >> On 26/05/2021 23:40, Beata Michalska wrote: >>> On Wed, May 26, 2021 at 08:17:41PM +0200, Dietmar Eggemann wrote: >>>> On 26/05/2021 14:51, Beata Michalska wrote: >>>>> On Wed, May 26, 2021 at 01:15:46PM +0100, Beata Michalska wrote: >>>>>> 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: [...] >>> We could possibly add a warning (like in EAS) if the asymmetry is detected >>> for SMT which would give some indication that there is smth ... wrong ? >> >> Maybe, in case you find an easy way to detect this. >> >> But the issue already exists today. Not with the topology mentioned >> above but in case we slightly change it to: >> >> cpus = { ([446 1024] [871 1024] [446 1024] ) ([1024 1024]) } >> ^^^^ >> so that we have a 1024 CPU in the lowest sd for each CPU, we would get >> SD_ASYM_CPUCAPACITY on SMT. > The asymmetry capacity flags are being set on a sched domain level, so > we could use the SD_SHARE_CPUCAPACITY|SD_SHARE_PKG_RESOURCES (cpu_smt_flags) > flags to determine if having asymmetry is valid or not ? If this is enough > this could be handled by the classify function? Or maybe something directly in sd_init(), like the WARN_ONCE() which triggers if somebody wants to sneak in a ~topology flag via a sched_domain_topology_level table? IMHO checking `SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY` will be sufficient here. diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 62d412013df8..77b73abbb9a4 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1561,6 +1561,11 @@ sd_init(struct sched_domain_topology_level *tl, sd_id = cpumask_first(sched_domain_span(sd)); sd->flags |= asym_cpu_capacity_classify(sd, cpu_map); + + WARN_ONCE((sd->flags & (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY)) == + (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY), + "CPU capacity asymmetry not supported on SMT\n"); + /* * Convert topological properties into behaviour. */ In case we can agree on something simple here I guess you can incorporate it into v7.