From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932146AbZJFKq2 (ORCPT ); Tue, 6 Oct 2009 06:46:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932122AbZJFKq1 (ORCPT ); Tue, 6 Oct 2009 06:46:27 -0400 Received: from smtp.nokia.com ([192.100.105.134]:36804 "EHLO mgw-mx09.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932109AbZJFKq1 (ORCPT ); Tue, 6 Oct 2009 06:46:27 -0400 Subject: Re: [BISECTED] "conservative" cpufreq governor broken From: Eero Nurkkala Reply-To: ext-eero.nurkkala@nokia.com To: ext Steven Noonan Cc: "linux-kernel@vger.kernel.org" , Thomas Gleixner , Rik van Riel , Venkatesh Pallipadi In-Reply-To: References: <1254814298.31336.63.camel@eenurkka-desktop> Content-Type: text/plain Organization: Nokia Date: Tue, 06 Oct 2009 13:43:15 +0300 Message-Id: <1254825795.31336.204.camel@eenurkka-desktop> Mime-Version: 1.0 X-Mailer: Evolution 2.26.1 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 06 Oct 2009 10:44:22.0918 (UTC) FILETIME=[F762DA60:01CA4671] X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2009-10-06 at 12:22 +0200, ext Steven Noonan wrote: > > I would suspect you have to have CONFIG_NO_HZ enabled to be able to > reproduce the issue (considering the title of the bisected commit and > my own config). Do you have it enabled? > Yes, it's enabled. > > And another round: > > > > cpufreq stats: OP1:16,78%, OP2:0,24%, OP3:5,14%, OP4:77,83% (72) > > > > Just once more after doing nothing: > > OP1:7,41%, OP2:0,11%, OP3:2,38%, OP4:90,10% (82) > > > > So I can't agree it's broken. The patch you bisected, actually filtered > > out such phenomenon, in which an IRQ made the cpufreq framework > > occasionally think we were idling, although we were not. So you got > > "bonus" idle time that shouldn't been there in the first place. Now that > > the "bonus" idle time is not there, your system load may indeed be so > > high that the system never spends 80% or more time in idle? Could that > > be the case? Of course, even though I can't agree it's broken, doesn't > > mean it isn't somehow broken ;) It'd be nice to get info on other > > systems as well... > > Interestingly, "ondemand" (the governor fixed by the bisected commit) > works fine. "conservative" is the only broken one. > If you took timestamps in /arch/x86/kernel/process_**.c: (let's assume process_64.c) in cpu_idle() around enter_idle(); and __exit_idle(), took the diff, added the diffs up, and compared it to system uptime, you could see how much time you spend in idle()? I think it's possible that even if the cpu load is near 0%, the system may idle only for a bare moment (that translates to a buggy pm_idle()), and time is spent elsewhere (less than 80% in idle). If I had similar findings like you, I'd be worried; but traces here and there will point out where things go wrong ;) - Eero