From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757608AbcIWE7r (ORCPT ); Fri, 23 Sep 2016 00:59:47 -0400 Received: from mail-pf0-f169.google.com ([209.85.192.169]:33215 "EHLO mail-pf0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752998AbcIWE7o (ORCPT ); Fri, 23 Sep 2016 00:59:44 -0400 Subject: Re: [PATCH 4/4] cpuidle/menu: add per cpu pm_qos_resume_latency consideration To: "Rafael J. Wysocki" , Vincent Guittot References: <1472114562-2736-1-git-send-email-alex.shi@linaro.org> <1472114562-2736-4-git-send-email-alex.shi@linaro.org> <57D80709.4040500@linaro.org> <3288596.DV966QMpDZ@vostro.rjw.lan> Cc: "Rafael J. Wysocki" , open list , "linux-pm@vger.kernel.org" , Ulf Hansson , Daniel Lezcano , Rasmus Villemoes , Arjan van de Ven , Rik van Riel From: Alex Shi Message-ID: <57E4B680.6080605@linaro.org> Date: Fri, 23 Sep 2016 12:58:40 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/23/2016 09:36 AM, Rafael J. Wysocki wrote: > On 9/14/2016 10:28 AM, Vincent Guittot wrote: >> Hi Rafael, >> >> On 14 September 2016 at 00:10, Rafael J. Wysocki >> wrote: >>> On Tuesday, September 13, 2016 10:02:49 PM Alex Shi wrote: >>>> Hi Daniel & Rafael, >>>> >>>> Any comments on this patch? >>> I actually am not sure about the whole series. >>> >>> I know your motivation, but honestly the changes here may not be the >>> best way >>> to achieve what you need. Is there some idea for better way? >>> >>> You may think that the changes are trivial, but in fact they are >>> not. There >>> are side effects and I'm not sure about the resulting user space >>> interface >>> at all. What's concern is abuse of user interface? If the request come from user level, is there other ways to set a value for this? >> This patchset has got 2 parts: >> - one part is about taking into account per-device resume latency >> constraint when selecting the idle state of a CPU. This value can >> already be set by kernel (even if it's probably not done yet) but this >> constraint is never taken into account >> - the other part is about exposing the resume latency to userspace. >> This part might raise more discussion but I see one example that could >> take advantage of this. When you have several clusters of CPUs and you >> want to dedicate some CPUs to latency sensitive activity and prevent >> deep sleep state on these CPUs but you want to let the other CPUs >> using all C-state > > The first very basic question about this I have is whether or not the > device PM QoS mechanism is suitable for the task at hand at all. > > It certainly hasn't been invented with it in mind. > Look though the device PM QoS, this kind of usage seems sensible. So why not? Regards Alex