From mboxrd@z Thu Jan 1 00:00:00 1970 From: Prarit Bhargava Subject: Re: [PATCH v2 0/4] cpufreq governors and Intel P state driver compatibility Date: Wed, 09 Dec 2015 08:12:37 -0500 Message-ID: <566828C5.3010605@redhat.com> References: <1449613890-10403-1-git-send-email-srinivas.pandruvada@linux.intel.com> <56676BAD.4030707@redhat.com> <1449619021.3240.209.camel@spandruv-desk3.jf.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:46552 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751310AbbLINMi (ORCPT ); Wed, 9 Dec 2015 08:12:38 -0500 In-Reply-To: <1449619021.3240.209.camel@spandruv-desk3.jf.intel.com> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Srinivas Pandruvada Cc: rafael.j.wysocki@intel.com, viresh.kumar@linaro.org, linux-pm@vger.kernel.org, trenn@suse.de On 12/08/2015 06:57 PM, Srinivas Pandruvada wrote: > On Tue, 2015-12-08 at 18:45 -0500, Prarit Bhargava wrote: >> >> On 12/08/2015 05:31 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. >>> >>> The reason Intel P state called powersave when it actually implemented >>> ondemand style P State selection, because the cpufreq core only allows >>> two generic policies "performance and powersave" for drivers which has >>> setpolicy() interface. All drivers using this interface are forced to >>> support these two policies. >>> >>> This patchset adds feature to have configurable generic policies and >>> allows ondemand as one of the policy. With this approach, Intel P state >>> now adds support for ondemand policy and power save policy both in >>> addition to performance. >> > Prarit, >> Srinivas, if I read the patchset correctly then this means that ondemand == >> powersave ? > Yes. Will it cause problem to you? Nope :) I like that option. I was just asking to make sure I understood the nature of the change. >> >> If so, is the intention to one day remove powersave altogether and switch to >> only ondemand & performance? > Yes. But we can add powersave, which all requests P state to max > efficiency ratio. But I want to check, if it will this cause more > confusion. > I'm thinking of end users -- we (Red Hat, but I'm pretty sure this applies to all distributions) have spent a significant amount of effort in educating users about the differences between the cpufreq and intel-pstate governors. Google search yields several results detailing the difference between the powersave and userspace governors as well, so I think that making changes at this point, especially after years of use, will only lead to more confusion for users. IOW, I agree with the technical argument, but I think that our users will really be confused. P.