From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sudeep Holla Subject: Re: [Eas-dev] [PATCH V3 2/3] cpufreq: schedutil: Process remote callback for shared policies Date: Thu, 20 Jul 2017 16:11:38 +0100 Message-ID: References: <3fbaa9aaba19bfff5ff25d2c4141e88fb83f1ea9.1499927699.git.viresh.kumar@linaro.org> <5968263D.1020801@codeaurora.org> <20170720122239.licc6yjd7jwipcvk@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20170720122239.licc6yjd7jwipcvk@hirez.programming.kicks-ass.net> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra , Saravana Kannan 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 List-Id: linux-pm@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