From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: cpuidle future and improvements Date: Mon, 18 Jun 2012 14:55:58 +0200 Message-ID: <4FDF255E.3080402@linaro.org> References: <4FDEE98D.7010802@linaro.org> <4FDF16DB.6080004@linux.vnet.ibm.com> <4FDF209E.7070803@linaro.org> <20120618125327.GB32111@tbergstrom-lnx.Nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail-lb0-f174.google.com ([209.85.217.174]:37150 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751042Ab2FRM4E (ORCPT ); Mon, 18 Jun 2012 08:56:04 -0400 Received: by lbbgm6 with SMTP id gm6so4269038lbb.19 for ; Mon, 18 Jun 2012 05:56:02 -0700 (PDT) In-Reply-To: <20120618125327.GB32111@tbergstrom-lnx.Nvidia.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Peter De Schrijver 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" On 06/18/2012 02:53 PM, Peter De Schrijver wrote: > 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 m= ay >>>> want to provide a different implementation. >>>> >>>> The Linaro Connect [3] event bring us the opportunity to meet peop= le >>>> involved in the power management and the cpuidle area for differen= t SoC. >>>> >>>> With the Tegra3 and big.LITTLE architecture, making per cpu latenc= ies >>>> 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 commo= n 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 o= n 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 implemen= t 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 clean= up >> and consolidate the code. For example, there is a dependency between >> acpi_idle and intel_idle which can be resolved with the notifiers, o= r >> there is intel specific code in cpuidle.c and cpuidle.h, cpu_relax i= s >> also introduced to cpuidle which is related to x86 not the cpuidle c= ore, >> 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 p= lace >> a cpuidle-next tree in order to consolidate all the cpuidle >> modifications people is willing to see upstream and provide better t= esting. >=20 > Sounds like a good idea. Do you have something like that already? Yes but I need to cleanup the tree before. http://git.linaro.org/gitweb?p=3Dpeople/dlezcano/linux-next.git;a=3Dsum= mary --=20 Linaro.org =E2=94=82 Open source software for= ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html