From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753235Ab1K1LDf (ORCPT ); Mon, 28 Nov 2011 06:03:35 -0500 Received: from e23smtp08.au.ibm.com ([202.81.31.141]:49960 "EHLO e23smtp08.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753134Ab1K1LDd (ORCPT ); Mon, 28 Nov 2011 06:03:33 -0500 Message-ID: <4ED36A7D.9070308@linux.vnet.ibm.com> Date: Mon, 28 Nov 2011 16:33:25 +0530 From: Deepthi Dharwar User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.23) Gecko/20110922 Thunderbird/3.1.15 MIME-Version: 1.0 Newsgroups: gmane.linux.power-management.general,gmane.linux.ports.ppc64.devel,gmane.linux.kernel To: Benjamin Herrenschmidt CC: linuxppc-dev@ozlabs.org, linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Subject: Re: [RFC PATCH v2 4/4] cpuidle: (POWER) Handle power_save=off References: <20111117112815.9191.2322.stgit@localhost6.localdomain6> <20111117112906.9191.54050.stgit@localhost6.localdomain6> <1322435233.23348.19.camel@pasglop> In-Reply-To: <1322435233.23348.19.camel@pasglop> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit x-cbid: 11112801-5140-0000-0000-000000542F2F Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/28/2011 04:37 AM, Benjamin Herrenschmidt wrote: > On Thu, 2011-11-17 at 16:59 +0530, Deepthi Dharwar wrote: >> This patch makes pseries_idle_driver not to be registered when >> power_save=off kernel boot option is specified. The >> boot_option_idle_override variable used here is similar to >> its usage on x86. > > Quick Q. With your changes, the CPU will never get into idle at all > until cpuidle initializes and the driver loads. > > That means not only much later in the boot process, but potentially > never if the distro has the driver as a module and fails to load it, or > similar. > > Can't that be an issue ? Shouldn't we keep at least one of the basic > idle functions as a fallback ? > On an LPAR if cpuidle is disabled, ppc_md.power_save is still set to cpuidle_idle_call by default here. This would result in calling of cpuidle_idle_call repeatedly, only for the call to return -ENODEV. The default idle is never executed. This would be a major design flaw. No fallback idle routine. We propose to fix this by checking the return value of ppc_md.power_save() call from void to int. Right now return value is void, but if we change this to int, this would solve two problems. One being removing the cast to a function pointer in the prev patch and this design flaw stated above. So by checking the return value of ppc_md.power_save(), we can invoke the default idle on failure. But my only concern is about the effects of changing the ppc_md.power_save() to return int on other powerpc architectures. Would it be a good idea to change the return type to int which would help us flag an error and fallback to default idle? > Cheers, > Ben. > > Regards, Deepthi