From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gautham R Shenoy Subject: Re: [v3 PATCH 2/3] powernv-cpufreq: Fix pstate_to_idx() to handle non-continguous pstates Date: Mon, 18 Dec 2017 14:08:20 +0530 Message-ID: <20171218083820.GA28881@in.ibm.com> References: <1513148261-21097-1-git-send-email-ego@linux.vnet.ibm.com> <1513148261-21097-3-git-send-email-ego@linux.vnet.ibm.com> Reply-To: ego@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Balbir Singh Cc: "Gautham R. Shenoy" , Shilpasri G Bhat , Viresh Kumar , "Rafael J. Wysocki" , huntbag@linux.vnet.ibm.com, Akshay Adiga , Michael Ellerman , Vaidyanathan Srinivasan , linux-pm@vger.kernel.org, "linux-kernel@vger.kernel.org" , "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" List-Id: linux-pm@vger.kernel.org Hi Balbir, On Sun, Dec 17, 2017 at 02:15:25PM +1100, Balbir Singh wrote: > On Wed, Dec 13, 2017 at 5:57 PM, Gautham R. Shenoy > wrote: > > From: "Gautham R. Shenoy" > > > > The code in powernv-cpufreq, makes the following two assumptions which > > are not guaranteed by the device-tree bindings: > > > > 1) Pstate ids are continguous: This is used in pstate_to_idx() to > > obtain the reverse map from a pstate to it's corresponding > > entry into the cpufreq frequency table. > > > > 2) Every Pstate should always lie between the max and the min > > pstates that are explicitly reported in the device tree: This > > is used to determine whether a pstate reported by the PMSR is > > out of bounds. > > > > Both these assumptions are unwarranted and can change on future > > platforms. > > While this is a good thing, I wonder if it is worth the complexity. Pstates > are contiguous because they define transitions in incremental value > of change in frequency and I can't see how this can be broken in the > future? In the future, we can have the OPAL firmware give us a smaller set of pstates instead of expose every one of them. As it stands today, for most of the workloads, we will need at best 20-30 pstates and not beyond that. > > Balbir Singh. > -- Thanks and Regards gautham.