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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 6CFF8C388F9 for ; Wed, 21 Oct 2020 17:23:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0B5FC2224E for ; Wed, 21 Oct 2020 17:23:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603301036; bh=xq9F3BNwrdzcMaeiCuh+tv2UemTAqtVTeWOtyKnQsxM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=avXKiBHiR4dBugb6Uuf9urrp62DoznXqlpahviD/r+odhzau8RmqgJI/ssJG+h/ge 0iyQozA29dThrXHzbUnCzcx4P7e3LhgM6hhQWFw1tlfxe09P/tqR34ngNwg1/+0v3D OJJotbiJ9kRx0fT45rfo+p6F2mTe5ZLFR25fkbqU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2502680AbgJURXx (ORCPT ); Wed, 21 Oct 2020 13:23:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:52316 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2503440AbgJURXw (ORCPT ); Wed, 21 Oct 2020 13:23:52 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 990332224E; Wed, 21 Oct 2020 17:23:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603301031; bh=xq9F3BNwrdzcMaeiCuh+tv2UemTAqtVTeWOtyKnQsxM=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=j+ncN65MDIe17KRnakxuyrEDqKSURzcGQnDCDtguNYVz5cMwquYGFvIsC9X1JESTi LIUDla4jGek6RZFQOW2xN+Am7dTAnKEtji9WiqXtqm/sdV9WYRg8eGetOQXovF36VS 1TI7oAb6XM+8lIKEuFc6ItikkaH/wNzlJgO8YoPs= Date: Wed, 21 Oct 2020 18:23:46 +0100 From: Will Deacon To: Qais Yousef Cc: Catalin Marinas , Marc Zyngier , "Peter Zijlstra (Intel)" , Morten Rasmussen , Greg Kroah-Hartman , Linus Torvalds , James Morse , linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org Subject: Re: [RFC PATCH v2 4/4] arm64: Export id_aar64fpr0 via sysfs Message-ID: <20201021172345.GF18071@willie-the-truck> References: <20201021104611.2744565-1-qais.yousef@arm.com> <20201021104611.2744565-5-qais.yousef@arm.com> <63fead90e91e08a1b173792b06995765@kernel.org> <20201021121559.GB3976@gaia> <20201021144112.GA17912@willie-the-truck> <20201021150313.ecxawwxsowweye43@e107158-lin> <20201021152310.GA18071@willie-the-truck> <20201021160730.komcgrp7q2tly55w@e107158-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201021160730.komcgrp7q2tly55w@e107158-lin> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Wed, Oct 21, 2020 at 05:07:30PM +0100, Qais Yousef wrote: > On 10/21/20 16:23, Will Deacon wrote: > > > > If a cpumask is easier to implement and easier to use, then I think that's > > > > what we should do. It's also then dead easy to disable if necessary by > > > > just returning 0. The only alternative I would prefer is not having to > > > > expose this information altogether, but I'm not sure that figuring this > > > > out from MIDR/REVIDR alone is reliable. > > > > > > I did suggest this before, but I'll try gain. If we want to assume a custom > > > bootloader and custom user space, we can make them provide the mask. > > > > Who mentioned a custom bootloader? In the context of Android, we're > > Custom bootloader as in a bootloader that needs to opt-in to enable the > feature (pass the right cmdline param). Catalin suggested to make this a sysctl > to allow also for runtime toggling. But the initial intention was to have this > to enable it at cmdline. Hmm, ok, I don't think allowing the cmdline to be specified means its a custom bootloader. > > talking about a user-space that already manages scheduling affinity. > > > > > For example, the new sysctl_enable_asym_32bit could be a cpumask instead of > > > a bool as it currently is. Or we can make it a cmdline parameter too. > > > In both cases some admin (bootloader or init process) has to ensure to fill it > > > correctly for the target platform. The bootloader should be able to read the > > > registers to figure out the mask. So more weight to make it a cmdline param. > > > > I think this is adding complexity for the sake of it. I'm much more in > > I actually think it reduces complexity. No special ABI to generate the mask > from the kernel. The same opt-in flag is the cpumask too. Maybe I'm misunderstanding your proposal but having a cpumask instead of a bool means you now have to consider policy on a per-cpu basis, which adds an extra dimension to this. For example, do you allow that mask to be changed at runtime so that differents sets of CPUs now support 32-bit? Do you preserve it across hotplug? Will