From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Date: Wed, 16 Mar 2016 22:32:46 +0100 Message-ID: <6960637.XgeniQrqfM@vostro.rjw.lan> References: <1457932932-28444-1-git-send-email-mturquette+renesas@baylibre.com> <56E9B7A1.5030806@arm.com> <20160316200752.GJ6344@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7Bit Return-path: Received: from v094114.home.net.pl ([79.96.170.134]:42005 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754487AbcCPVao (ORCPT ); Wed, 16 Mar 2016 17:30:44 -0400 In-Reply-To: <20160316200752.GJ6344@twins.programming.kicks-ass.net> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Peter Zijlstra Cc: Dietmar Eggemann , Michael Turquette , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Juri.Lelli@arm.com, steve.muckle@linaro.org, morten.rasmussen@arm.com, vincent.guittot@linaro.org, Michael Turquette On Wednesday, March 16, 2016 09:07:52 PM Peter Zijlstra wrote: > On Wed, Mar 16, 2016 at 07:44:33PM +0000, Dietmar Eggemann wrote: > > intel_pstate (setpolicy()) is an exception but my humble guess is that > > systems with intel_pstate driver have X86_FEATURE_APERFMPERF support. > > A quick browse of the Intel SDM says you're right. It looks like > everything after Pentium-M; so Core-Solo/Core-Duo and onwards have > APERF/MPERF. > > And it looks like P6 class systems didn't have DVFS support at all, > which basically leaves P4 and Pentium-M as the only chips to have DVFS > support lacking APERF/MPERF. > > And while I haven't got any P4 based space heaters left, I might still > have a Pentium-M class laptop somewhere (if it still boots). intel_pstate depends on APERF/MPERF, so it won't work with anything without them.