From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030476AbcIWBgk (ORCPT ); Thu, 22 Sep 2016 21:36:40 -0400 Received: from mga14.intel.com ([192.55.52.115]:36302 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965135AbcIWBgg (ORCPT ); Thu, 22 Sep 2016 21:36:36 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.30,380,1470726000"; d="scan'208";a="172191449" Subject: Re: [PATCH 4/4] cpuidle/menu: add per cpu pm_qos_resume_latency consideration To: 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" , Alex Shi , open list , "linux-pm@vger.kernel.org" , Ulf Hansson , Daniel Lezcano , Rasmus Villemoes , Arjan van de Ven , Rik van Riel From: "Rafael J. Wysocki" Organization: Intel Technology Poland Sp. z o. o., KRS 101882, ul. Slowackiego 173, 80-298 Gdansk Message-ID: Date: Fri, 23 Sep 2016 03:36:30 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. >> >> 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. > 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. Thanks, Rafael