From mboxrd@z Thu Jan 1 00:00:00 1970 From: Deepthi Dharwar Subject: Re: [RFC PATCH v2 4/4] cpuidle: (POWER) Handle power_save=off Date: Mon, 28 Nov 2011 16:33:25 +0530 Message-ID: <4ED36A7D.9070308__30833.3199973733$1322478237$gmane$org@linux.vnet.ibm.com> References: <20111117112815.9191.2322.stgit@localhost6.localdomain6> <20111117112906.9191.54050.stgit@localhost6.localdomain6> <1322435233.23348.19.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1322435233.23348.19.camel@pasglop> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: linux-pm-bounces@lists.linux-foundation.org Errors-To: linux-pm-bounces@lists.linux-foundation.org To: Benjamin Herrenschmidt Cc: linuxppc-dev@ozlabs.org, linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org List-Id: linux-pm@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