From patchwork Thu Sep 24 12:30:14 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ionela Voinescu X-Patchwork-Id: 11797165 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 6E0ED6CB for ; Thu, 24 Sep 2020 12:30:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 58F492388A for ; Thu, 24 Sep 2020 12:30:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727749AbgIXMao (ORCPT ); Thu, 24 Sep 2020 08:30:44 -0400 Received: from foss.arm.com ([217.140.110.172]:44598 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727561AbgIXMao (ORCPT ); Thu, 24 Sep 2020 08:30:44 -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 A9515113E; Thu, 24 Sep 2020 05:30:43 -0700 (PDT) Received: from e108754-lin.cambridge.arm.com (unknown [10.1.199.49]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 1DC063F73B; Thu, 24 Sep 2020 05:30:42 -0700 (PDT) From: Ionela Voinescu To: catalin.marinas@arm.com, sudeep.holla@arm.com, will@kernel.org, linux@armlinux.org.uk, rjw@rjwysocki.net, viresh.kumar@linaro.org Cc: dietmar.eggemann@arm.com, valentin.schneider@arm.com, linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, ionela.voinescu@arm.com Subject: [PATCH 0/2]cpufreq,topology,arm: disable FI for BL_SWITCHER Date: Thu, 24 Sep 2020 13:30:14 +0100 Message-Id: <20200924123016.13427-1-ionela.voinescu@arm.com> X-Mailer: git-send-email 2.17.1 Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org This series is the result of the discussions ([1], [2]) around the complications that the BL_SWITCHER poses when it comes to Frequency Invariance (FI) and it aims to restart the discussions. To properly scale its per-entity load-tracking signals, the task scheduler needs to be given a frequency scale factor, i.e. some image of the current frequency the CPU is running at, relative to its maximum frequency. But (reiterating the message in the changelog of patch 2/2), big.LITTLE switching complicates the setting of a correct cpufreq-based frequency invariance scale factor due to (as observed in drivers/cpufreq/vexpress-spc-cpufreq.c): - Incorrect current and maximum frequencies as a result of the exposure of a virtual frequency table to the cpufreq core, - Missed updates as a result of asynchronous frequency adjustments caused by frequency changes in other CPU pairs. More information on this feature can be found at [3]. Given that its functionality is atypical in regards to FI and that this is an old technology, patch 2/2 disable FI for when big.LITTLE switching is configured in to prevent incorrect scale setting. For this purpose patch 1/2 changes the way arch_set_freq_scale() is defined in architecture code which brings it in line with the logic of other architectural function definitions while allowing for less invasive filtering of FI support. In the discussions at [2], three possible solutions were suggested: - (1) conditioning FI by !CONFIG_BL_SWITCHER - (2) leave as is with note in driver specifying this FI broken functionality - (3) removing full BL_SWITCHER support This series restructures the solution at (1). The reason for it is that the new patch limits the ifdef filtering to the arm topology include file, a location where frequency invariance functions are defined. Therefore, this seems more appropriate given that the b.L switcher is an arm technology and that the new FI filtering location seems more natural for conditioned FI disabling. Solutions (2) and (3) were not implemented given that there might be some remaining users of this technology (Samsung Chromebook 2 - Samsung Exynos 5 Octa 5420, Samsung Exynos 5 Octa 5800) and therefore leaving this broken (2) seems equally bad to removing support for it (3). [1] https://lore.kernel.org/lkml/20200701090751.7543-5-ionela.voinescu@arm.com/ [2] https://lore.kernel.org/lkml/20200722093732.14297-4-ionela.voinescu@arm.com/ [3] https://lwn.net/Articles/481055/ Many thanks, Ionela. Ionela Voinescu (2): cpufreq,arm,arm64: restructure definitions of arch_set_freq_scale() arm: disable frequency invariance for CONFIG_BL_SWITCHER arch/arm/include/asm/topology.h | 4 ++++ arch/arm64/include/asm/topology.h | 1 + drivers/base/arch_topology.c | 4 ++-- drivers/cpufreq/cpufreq.c | 7 ------- include/linux/arch_topology.h | 2 ++ include/linux/cpufreq.h | 11 ++++++++--- 6 files changed, 17 insertions(+), 12 deletions(-) Acked-by: Sudeep Holla (BL_SWITCHER and topology parts)