From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753304Ab2GRLMV (ORCPT ); Wed, 18 Jul 2012 07:12:21 -0400 Received: from toro.web-alm.net ([62.245.132.31]:53608 "EHLO toro.web-alm.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752076Ab2GRLMR (ORCPT ); Wed, 18 Jul 2012 07:12:17 -0400 Message-ID: <500697A9.6070101@osadl.org> Date: Wed, 18 Jul 2012 13:02:01 +0200 From: Carsten Emde Organization: Open Source Automation Development Lab (OSADL) User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.24) Gecko/20111108 Fedora/3.1.16-1.fc14 Thunderbird/3.1.16 MIME-Version: 1.0 To: Deepthi Dharwar CC: Len Brown , Kevin Hilman , Thomas Gleixner , LKML Subject: Re: [PATCH 1/1] Honor state disabling in the cpuidle ladder governor References: <20120717185914.063547728@osadl.org> <20120717190330.700421963@osadl.org> <50065953.9040904@linux.vnet.ibm.com> In-Reply-To: <50065953.9040904@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/18/2012 08:36 AM, Deepthi Dharwar wrote: > On 07/18/2012 12:29 AM, Carsten Emde wrote: > >> There are two cpuidle governors ladder and menu. While the ladder >> governor is always available, if CONFIG_CPU_IDLE is selected, the >> menu governor additionally requires CONFIG_NO_HZ. >> >> A particular C state can be disabled by writing to the sysfs file >> /sys/devices/system/cpu/cpuN/cpuidle/stateN/disable, but this mechanism >> is only implemented in the menu governor. Thus, in a system where >> CONFIG_NO_HZ is not selected, the ladder governor becomes default and >> always will walk through all sleep states - irrespective of whether the >> C state was disabled via sysfs or not. The only way to select a specific >> C state was to write the related latency to /dev/cpu_dma_latency and >> keep the file open as long as this setting was required - not very >> practical and not suitable for setting a single core in an SMP system. >> >> With this patch, the ladder governor only will promote to the next >> C state, if it has not been disabled, and it will demote, if the >> current C state was disabled. > > Yes, I agree that currently that disabling a particular C-state > is not reflected in working of ladder governor. This patch is needed > to fix it on ladder too. > > Also wanted to clarify on the intended implementation here, > if there are say 5 C-states on a system, disabling 2nd > state would also end by disabling all the remaining 3 deeper states too > as ladder governor enters the lightest state first, and will only move > on to the next deeper state if a idle period was long enough as > per the implementation. > If one is disabling only the deepest state, then it would > work as intended. Yes, the patch does not make the setting of the sysfs variable "disable" coherent, i.e. if one is disabling a light state, then all deeper states are disabled as well, but the "disable" variable does not reflect it. Likewise, if one enables a deep state but a lighter state still is disabled, then this has no effect. I could implement a sanitize mechanism of the ladder governor that takes care the "disable" variables of all deeper states are set to 1, if a state is disabled, and those of all lighter states are set to 0, if a state is enabled. Do you wish me to do that? -Carsten.