From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263254AbTJUT4L (ORCPT ); Tue, 21 Oct 2003 15:56:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263282AbTJUT4L (ORCPT ); Tue, 21 Oct 2003 15:56:11 -0400 Received: from sccrmhc11.comcast.net ([204.127.202.55]:56007 "EHLO sccrmhc11.comcast.net") by vger.kernel.org with ESMTP id S263254AbTJUT4I (ORCPT ); Tue, 21 Oct 2003 15:56:08 -0400 Message-ID: <1066766155.a66ff46274f08@carlthompson.net> X-Priority: 3 (Normal) Date: Tue, 21 Oct 2003 12:55:55 -0700 From: Carl Thompson To: "Nakajima, Jun" Cc: arjanv@redhat.com, "Pallipadi, Venkatesh" , "Mallick, Asit K" , Dominik Brodowski , linux-acpi , cpufreq@www.linux.org.uk, linux-kernel@vger.kernel.org Subject: RE: [PATCH] 3/3 Dynamic cpufreq governor and updates to ACPIP-state driver References: <7F740D512C7C1046AB53446D3720017304B031@scsmsx402.sc.intel.com> In-Reply-To: <7F740D512C7C1046AB53446D3720017304B031@scsmsx402.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Disposition: inline Content-Transfer-Encoding: 7bit User-Agent: Internet Messaging Program (IMP) 4.0-cvs X-Originating-IP: 192.168.0.174 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Quoting "Nakajima, Jun" : > ... > It's about the frequency of the feedback loop. As we have much lower > latency with P-state transitions, the sampling time can be order of > millisecond (or shorter if meaningful). A userland daemon can have a > high-level policy (preferences, or set of parameters), but it cannot be > part of the real feedback loop. If we combine P-state transitions and > deeper C-state transitions, the situation is worse with a userland > daemon. You are making the assumption that a higher polling frequency (we'll say 1ms) is in general better than a lower frequency (we'll say 1s). I submit that it is not. If I hit a key on my keyboard and your high frequency loop increases CPU speed so that my word processor displays the letter 0.01s faster, is that really beneficial? If a window renders in 0.2s seconds instead of 0.3s is that a difference I am going to notice? On the other hand, if I do a kernel compile and it is done 0.999s faster with the higher frequency loop, am I going to miss that second over such a long duration? (In reality, the compile with the high-frequency loop would probably take longer unless it has near zero overhead). In my opinion it is wasteful to increase CPU speed unless there is a longer term need for it. > Jun Carl Thompson