From mboxrd@z Thu Jan 1 00:00:00 1970 From: Srinivas Pandruvada Subject: Re: [PATCH 0/4] cpufreq governors and Intel P state driver compatibility Date: Wed, 09 Dec 2015 08:12:54 -0800 Message-ID: <1449677574.4180.11.camel@linux.intel.com> References: <1449274118-15575-1-git-send-email-srinivas.pandruvada@linux.intel.com> <3480094.iq1rZTMoWu@skinner> <1449596583.3240.158.camel@spandruv-desk3.jf.intel.com> <2157917.dlSdjkkIZW@skinner> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mga14.intel.com ([192.55.52.115]:25987 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751779AbbLIQP3 (ORCPT ); Wed, 9 Dec 2015 11:15:29 -0500 In-Reply-To: <2157917.dlSdjkkIZW@skinner> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Thomas Renninger Cc: rjw@rjwysocki.net, len.brown@intel.com, viresh.kumar@linaro.org, linux-pm@vger.kernel.org On Wed, 2015-12-09 at 16:02 +0100, Thomas Renninger wrote: > On Tuesday, December 08, 2015 09:43:03 AM Srinivas Pandruvada wrote: > > On Tue, 2015-12-08 at 15:35 +0100, Thomas Renninger wrote: > > > On Friday, December 04, 2015 04:08:34 PM Srinivas Pandruvada > > > wrote: > > > > Intel P State driver implements two policies, performance and > > > > powersave. > > > > The powersave policy is similar to ondemand cpufreq governor > > > > when using > > > > acpi-cpufreq. This causes lots of confusion among users. This > > > > results > > > > in invalid comparison of performance when acpi-cpufreq and > > > > Intel P state > > > > performance is compared. > > > > > > After several years you want to change this again? > > > > This is based on feedback. But again, if this breaks some users, > > then we > > need to think. > > > > > We released documentation for this for SLE 12 recently. > > > It was not that easy to phrase, but it would be wrong again with > > > newer > > > kernels..., sigh. > > > > Will this patchset break SLE 12? > > Are you defaulting to "powersave" policy of Intel P state? > > We use powersave as default with intel_pstate because this is > default. > > You won't "break" SLE 12 and I mostly thought about documentation. > This is the intel_pstate part: > > ------------------------------------- > Not all drivers use the in-kernel governors to dynamically scale > power > frequency at runtime. For example, the intel_pstate driver adjusts > power > frequency itself. Use the cpupower frequency-info command to find out > which > driver your system uses. > ------------------------------------- > > Fortunately we cut out the part to explain why "powersave" governor > shows > up and what it does. So we are more or less safe. > > Still.., instead of providing the next quick shot, we may want to > think > further... > Having an ondemand governor and a faked may lead to more confusion in > the > future. May be calling "intel_pstate_ondemand" instead of powersave. But that needs lots of changes in cpufreq core or we have to implement this driver as a governor + cpufreq driver with target() I/F like acpi -cpufreq. > In general, worst that can happen for SLE (probably same for RHEL) > are any > kind of performance regressions that are introduced by trying to save > more > power (on the same HW). > Customers/users will find them and complain and need at least a param > to > get back to old (power wasting) behaviour. > I didn't get this point. Thanks, Srinivas > Thomas >