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: Wed, 10 Jan 2018 14:25:45 +0530 Message-ID: <20180110085545.GA13666@in.ibm.com> References: <1513148261-21097-1-git-send-email-ego@linux.vnet.ibm.com> <20171218083820.GA28881@in.ibm.com> <3110289.BbUpyYVBQa@aspire.rjw.lan> 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: "Rafael J. Wysocki" , Gautham R Shenoy , Shilpasri G Bhat , Viresh Kumar , Abhishek , 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 Rafael, On Wed, Jan 03, 2018 at 11:47:58PM +1100, Balbir Singh wrote: > On Wed, Jan 3, 2018 at 11:07 PM, Rafael J. Wysocki wrote: > > On Monday, December 18, 2017 9:38:20 AM CET Gautham R Shenoy wrote: > >> 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. > > > > I'm not sure about the status here. > > > > Is this good to go as is or is it going to be updated? > > > > I have no major objections, except some of the added complexity, but > Gautham makes a point that this is refactoring for the future I have tested this across POWER8 and POWER9. The additional complexity introduced by the second patch is required for the future when we are going to reduce the number of pstates. > > Balbir Singh. > -- Thanks and Regards gautham.