From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751159AbdFBJUP (ORCPT ); Fri, 2 Jun 2017 05:20:15 -0400 Received: from foss.arm.com ([217.140.101.70]:37542 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910AbdFBJUN (ORCPT ); Fri, 2 Jun 2017 05:20:13 -0400 Cc: Sudeep Holla , leo.yan@linaro.org, "open list:CPUIDLE DRIVERS" , open list Subject: Re: [PATCH V2] ARM: cpuidle: Support asymmetric idle definition To: Daniel Lezcano , rjw@rjwysocki.net, lorenzo.pieralisi@arm.com References: <1496317188-15272-1-git-send-email-daniel.lezcano@linaro.org> From: Sudeep Holla Organization: ARM Message-ID: <3ec88de3-7d18-0ea6-bc27-e98084f2b6f6@arm.com> Date: Fri, 2 Jun 2017 10:20:09 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: <1496317188-15272-1-git-send-email-daniel.lezcano@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/06/17 12:39, Daniel Lezcano wrote: > Some hardware have clusters with different idle states. The current code does > not support this and fails as it expects all the idle states to be identical. > > Because of this, the Mediatek mtk8173 had to create the same idle state for a > big.Little system and now the Hisilicon 960 is facing the same situation. > > Solve this by simply assuming the multiple driver will be needed for all the > platforms using the ARM generic cpuidle driver which makes sense because of the > different topologies we can support with a single kernel for ARM32 or ARM64. > > Every CPU has its own driver, so every single CPU can specify in the DT the > idle states. > > This simple approach allows to support the future dynamIQ system, current SMP > and HMP. > > It is unoptimal from a memory point of view for a system with a large number of > CPUs but nowadays there is no such system with a cpuidle driver on ARM. > While I agree this may be simple solution, but just not necessary for systems with symmetric idle states especially one with large number of CPUs. I don't like to see 96 CPU Idle driver on say ThunderX. So we *must* have some basic distinction done here. IMO, we can't punish a large SMP systems just because they don't have asymmetric idle states. -- Regards, Sudeep