From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754135Ab2GRLtG (ORCPT ); Wed, 18 Jul 2012 07:49:06 -0400 Received: from e28smtp09.in.ibm.com ([122.248.162.9]:45000 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754029Ab2GRLtC (ORCPT ); Wed, 18 Jul 2012 07:49:02 -0400 Message-ID: <5006A2A6.8030902@linux.vnet.ibm.com> Date: Wed, 18 Jul 2012 17:18:54 +0530 From: Deepthi Dharwar User-Agent: Mozilla/5.0 (X11; Linux i686; rv:11.0) Gecko/20120329 Thunderbird/11.0.1 MIME-Version: 1.0 To: Carsten Emde CC: Len Brown , Kevin Hilman , Thomas Gleixner , LKML , Linux PM mailing list 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> <500697A9.6070101@osadl.org> In-Reply-To: <500697A9.6070101@osadl.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit x-cbid: 12071811-2674-0000-0000-0000054AE9FC Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/18/2012 04:32 PM, Carsten Emde wrote: > 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. Agree, as per the ladder design. > 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? > No, I dont think thats necessary, current code suffices it. The disable flag is knob we are giving to the user . So may be just document the intended use of disable flag working alongside design of ladder governor. Cheers Deepthi > -Carsten. >