From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936313AbdGTPLp (ORCPT ); Thu, 20 Jul 2017 11:11:45 -0400 Received: from foss.arm.com ([217.140.101.70]:55560 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934593AbdGTPLo (ORCPT ); Thu, 20 Jul 2017 11:11:44 -0400 Cc: Sudeep Holla , Viresh Kumar , Rafael Wysocki , Ingo Molnar , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, smuckle.linux@gmail.com, eas-dev@lists.linaro.org Subject: Re: [Eas-dev] [PATCH V3 2/3] cpufreq: schedutil: Process remote callback for shared policies To: Peter Zijlstra , Saravana Kannan References: <3fbaa9aaba19bfff5ff25d2c4141e88fb83f1ea9.1499927699.git.viresh.kumar@linaro.org> <5968263D.1020801@codeaurora.org> <20170720122239.licc6yjd7jwipcvk@hirez.programming.kicks-ass.net> From: Sudeep Holla Organization: ARM Message-ID: Date: Thu, 20 Jul 2017 16:11:38 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170720122239.licc6yjd7jwipcvk@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/07/17 13:22, Peter Zijlstra wrote: > On Thu, Jul 13, 2017 at 07:02:37PM -0700, Saravana Kannan wrote: >> In all Qualcomm chipsets (well, at least the ones that have been used in >> Android devices so far), we can switch the frequency of any CPU from any >> other CPU. If we can do that even without fast switching, why wouldn't any >> theoretical fast switching be incapable of supporting this? Is this a >> limitation specific to x86 that we are assuming all architectures and >> platforms are going to have? > > So the typical implementation of fast switching we're thinking of is the > CPU writing the DVFS request into a machine register. Now machine > registers are typically per logical CPU. > But, if ARM decides to architect and move to it to a system/machine register, we will end up with the same limitation :( IMO. For now with SCMI kind of interface, there's no such limitation as yoalready mentioned in the follow up email. -- Regards, Sudeep