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=-4.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 CB75CC47095 for ; Wed, 7 Oct 2020 14:34:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6EB12208C7 for ; Wed, 7 Oct 2020 14:34:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602081298; bh=yxJRNDxnbzWgYfu9mI4jTBn2/dLvCzBPtRUwDvF9ikY=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=dMfD+L6Qe+XbRuogKMTZZX2NWCP5NvCV+08UyNb8xHgmb2X/liCMMcDhLnLUDqdUg pliU6HGX8rDtl4T/pRRzeH4cOFgB4R5J+8wai9XgTC+76EIsZVu37buTYOSwukwaV6 BCGaS6usCL5cQogbfsWXEIssvjASAIKeQZHcLUK4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728655AbgJGOe5 (ORCPT ); Wed, 7 Oct 2020 10:34:57 -0400 Received: from mail-ot1-f67.google.com ([209.85.210.67]:43281 "EHLO mail-ot1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728535AbgJGOe5 (ORCPT ); Wed, 7 Oct 2020 10:34:57 -0400 Received: by mail-ot1-f67.google.com with SMTP id n61so2377764ota.10; Wed, 07 Oct 2020 07:34:56 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=PgDc8dM2xrjB20bw4f4PiZlRABZ5H2dY1eMkVvg7OTU=; b=ZiliCAk5eFLadW2BHu6zBenHCg99TiXL9geEI4s9rQOC3iZ+EeY2IFXfiGBa1mSmQL hrisOTb1LaiuzZ30PMm3wzWJ6Qr5a5n+4FCABlQk+v5puwFz4hGe9T9sXx0eTybNSYaQ Iy+BRx6ch0i7XbAW8FbyfJ0MvYj1ROACtvvOBe6j/yaR799imf2tskwGIU5enUB9dhXb 6BSrKFYGH5y09YHbmjjnXPLHKroYVHB6WTK4VqzmNP4WqxHjbESu0T8Pv50IIvy+W/Ng dEBSn7whu8whe1ujAG9/PJs7fu4MUEQwCtAgLbFGqrWP/JfIQcVPnIv2qHQmLMfN+zfp 52Hg== X-Gm-Message-State: AOAM530Mn+hxadM3Jkv2G85ONI5cxFkfUlU+4+cSUGjHcFjrwU+920YD X15BQAWwc5chuhF5UElOV7/kikSQbLTikH0aa9Y= X-Google-Smtp-Source: ABdhPJzu23bGwguFFrdflPnWMvQ9i8Nmkl4xL/jF3WIk7+7lZcfnMh87Zsp+cw/WRcpil19L3vljSNpmkgIAa3oLSbc= X-Received: by 2002:a9d:3626:: with SMTP id w35mr2148009otb.206.1602081295952; Wed, 07 Oct 2020 07:34:55 -0700 (PDT) MIME-Version: 1.0 References: <20200924123016.13427-1-ionela.voinescu@arm.com> In-Reply-To: <20200924123016.13427-1-ionela.voinescu@arm.com> From: "Rafael J. Wysocki" Date: Wed, 7 Oct 2020 16:34:44 +0200 Message-ID: Subject: Re: [PATCH 0/2]cpufreq,topology,arm: disable FI for BL_SWITCHER To: Ionela Voinescu , Catalin Marinas , Sudeep Holla Cc: Will Deacon , Russell King - ARM Linux , "Rafael J. Wysocki" , Viresh Kumar , Dietmar Eggemann , Valentin Schneider , Linux PM , Linux ARM , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 24, 2020 at 2:30 PM Ionela Voinescu wrote: > > 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/ I can take this set with the ACKs from Viresh if that's fine by everyone. Catalin? Sudeep?