Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751857Ab2FRMyX (ORCPT ); Mon, 18 Jun 2012 08:54:23 -0400 Received: from hqemgate04.nvidia.com ([216.228.121.35]:17320 "EHLO hqemgate04.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751178Ab2FRMyV (ORCPT ); Mon, 18 Jun 2012 08:54:21 -0400 X-PGP-Universal: processed; by hqnvupgp06.nvidia.com on Mon, 18 Jun 2012 05:54:04 -0700 Date: Mon, 18 Jun 2012 15:53:27 +0300 From: Peter De Schrijver To: Daniel Lezcano CC: Deepthi Dharwar , "linux-acpi@vger.kernel.org" , "linux-pm@lists.linux-foundation.org" , Lists Linaro-dev , Linux Kernel Mailing List , Amit Kucheria , "lenb@kernel.org" , Andrew Morton , Linus Torvalds , Colin Cross , Rob Lee , "rjw@sisk.pl" , Kevin Hilman , "linux-next@vger.kernel.org" Subject: Re: cpuidle future and improvements Message-ID: <20120618125327.GB32111@tbergstrom-lnx.Nvidia.com> References: <4FDEE98D.7010802@linaro.org> <4FDF16DB.6080004@linux.vnet.ibm.com> <4FDF209E.7070803@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <4FDF209E.7070803@linaro.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3102 Lines: 72 On Mon, Jun 18, 2012 at 02:35:42PM +0200, Daniel Lezcano wrote: > On 06/18/2012 01:54 PM, Deepthi Dharwar wrote: > > On 06/18/2012 02:10 PM, Daniel Lezcano wrote: > > > >> > >> Dear all, > >> > >> A few weeks ago, Peter De Schrijver proposed a patch [1] to allow per > >> cpu latencies. We had a discussion about this patchset because it > >> reverse the modifications Deepthi did some months ago [2] and we may > >> want to provide a different implementation. > >> > >> The Linaro Connect [3] event bring us the opportunity to meet people > >> involved in the power management and the cpuidle area for different SoC. > >> > >> With the Tegra3 and big.LITTLE architecture, making per cpu latencies > >> for cpuidle is vital. > >> > >> Also, the SoC vendors would like to have the ability to tune their cpu > >> latencies through the device tree. > >> > >> We agreed in the following steps: > >> > >> 1. factor out / cleanup the cpuidle code as much as possible > >> 2. better sharing of code amongst SoC idle drivers by moving common bits > >> to core code > >> 3. make the cpuidle_state structure contain only data > >> 4. add a API to register latencies per cpu > > > > On huge systems especially servers, doing a cpuidle registration on a > > per-cpu basis creates a big overhead. > > So global registration was introduced in the first place. > > > > Why not have it as a configurable option or so ? > > Architectures having uniform cpuidle state parameters can continue to > > use global registration, else have an api to register latencies per cpu > > as proposed. We can definitely work to see the best way to implement it. > > Absolutely, this is one reason I think adding a function: > > cpuidle_register_latencies(int cpu, struct cpuidle_latencies); > > makes sense if it is used only for cpus with different latencies. > The other architecture will be kept untouched. > > IMHO, before adding more functionalities to cpuidle, we should cleanup > and consolidate the code. For example, there is a dependency between > acpi_idle and intel_idle which can be resolved with the notifiers, or > there is intel specific code in cpuidle.c and cpuidle.h, cpu_relax is > also introduced to cpuidle which is related to x86 not the cpuidle core, > etc ... > > Cleanup the code will help to move the different bits from the arch > specific code to the core code and reduce the impact of the core's > modifications. That should let a common pattern to emerge and will > facilitate the modifications in the future (per cpu latencies is one of > them). > > That will be a lot of changes and this is why I proposed to put in place > a cpuidle-next tree in order to consolidate all the cpuidle > modifications people is willing to see upstream and provide better testing. Sounds like a good idea. Do you have something like that already? Thanks, Peter. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/