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=-6.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT autolearn=ham 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 9D693C43381 for ; Wed, 27 Mar 2019 10:56:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6E72B2082F for ; Wed, 27 Mar 2019 10:56:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733019AbfC0K4q (ORCPT ); Wed, 27 Mar 2019 06:56:46 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:52618 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729489AbfC0K4q (ORCPT ); Wed, 27 Mar 2019 06:56:46 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id EA236A78; Wed, 27 Mar 2019 03:56:45 -0700 (PDT) Received: from queper01-lin (queper01-lin.cambridge.arm.com [10.1.195.48]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 256363F557; Wed, 27 Mar 2019 03:56:44 -0700 (PDT) Date: Wed, 27 Mar 2019 10:56:42 +0000 From: Quentin Perret To: Lingutla Chandrasekhar Cc: sudeep.holla@arm.com, dietmar.eggemann@arm.com, gregkh@linuxfoundation.org, will.deacon@arm.com, catalin.marinas@arm.com, morten.rasmussen@arm.com, linux-arm-kernel@lists.infradead.org, jeremy.linton@arm.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] arch_topology: Make cpu_capacity sysfs node as ready-only Message-ID: <20190327105640.ibiw5mvuggp35msl@queper01-lin> References: <1552048728-29657-1-git-send-email-clingutla@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1552048728-29657-1-git-send-email-clingutla@codeaurora.org> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Friday 08 Mar 2019 at 18:08:48 (+0530), Lingutla Chandrasekhar wrote: > If user updates any cpu's cpu_capacity, then the new value is going to > be applied to all its online sibling cpus. But this need not to be correct > always, as sibling cpus (in ARM, same micro architecture cpus) would have > different cpu_capacity with different performance characteristics. > So updating the user supplied cpu_capacity to all cpu siblings > is not correct. > > And another problem is, current code assumes that 'all cpus in a cluster > or with same package_id (core_siblings), would have same cpu_capacity'. > But with commit '5bdd2b3f0f8 ("arm64: topology: add support to remove > cpu topology sibling masks")', when a cpu hotplugged out, the cpu > information gets cleared in its sibling cpus. So user supplied > cpu_capacity would be applied to only online sibling cpus at the time. > After that, if any cpu hot plugged in, it would have different cpu_capacity > than its siblings, which breaks the above assumption. > > So instead of mucking around the core sibling mask for user supplied > value, use device-tree to set cpu capacity. And make the cpu_capacity > node as read-only to know the assymetry between cpus in the system. > While at it, remove cpu_scale_mutex usage, which used for sysfs write > protection. > > Tested-by: Dietmar Eggemann > Acked-by: Sudeep Holla > Signed-off-by: Lingutla Chandrasekhar Reviewed-by: Quentin Perret Tested-by: Quentin Perret Thanks for doing this, Quentin