From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Hilman Subject: Re: [PATCH RFC 3/3] PM / Domains: Introduce generic PM domain for cpu domain Date: Wed, 10 Jun 2015 10:01:10 -0700 Message-ID: <7hbngnpkfd.fsf@deeprootsystems.com> References: <1433456946-53296-1-git-send-email-lina.iyer@linaro.org> <1433456946-53296-4-git-send-email-lina.iyer@linaro.org> <5574121F.2000806@samsung.com> Mime-Version: 1.0 Content-Type: text/plain Return-path: Received: from mail-pd0-f176.google.com ([209.85.192.176]:36631 "EHLO mail-pd0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933947AbbFJRBO (ORCPT ); Wed, 10 Jun 2015 13:01:14 -0400 Received: by pdjm12 with SMTP id m12so41618210pdj.3 for ; Wed, 10 Jun 2015 10:01:13 -0700 (PDT) In-Reply-To: <5574121F.2000806@samsung.com> (Krzysztof Kozlowski's message of "Sun, 07 Jun 2015 18:42:55 +0900") Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Krzysztof Kozlowski Cc: Lina Iyer , rjw@rjwysocki.net, ulf.hansson@linaro.org, mathieu.poirier@linaro.org, linux-pm@vger.kernel.org, galak@codeaurora.org, msivasub@codeaurora.org, agross@codeaurora.org, linux-arm-kernel@lists.infradead.org Krzysztof Kozlowski writes: > W dniu 05.06.2015 o 07:29, Lina Iyer pisze: >> Generally cpus are grouped under a power domain in a SoC. When all cpus >> in the domain are in their power off state, > > What do you exactly mean here by "CPU in power off state"? How does it > map to kernel understanding of CPU device (hotplug? cpuidle?)? > >> the cpu domain can also be >> powered off. Genpd provides the framework for defining cpus as devices >> that are part of a cpu domain. > > The problem which is solved looks to me like the same problem which > coupled cpuidle tried to solve: a certain deep sleep mode (e.g. power > off) can be entered when whole cluster is idle or other CPUs in cluster > are powered off completely. > > It seems a little like duplicating the effort around coupled cpuidle. Yes, it duplicates some aspects of coupled idle states, but coupled states have their own limitations: - only handles CPUs, not other devices sharing a power rail (e.g. L2$, GIC, floating point unit, CoreSight, etc. etc.) - not scaling well past 2 CPUs - doesn't handle clusters: While this series only addresses CPUs currently, the approach can be extended. Because genpd handles nested domains, the could be used to model clusters as well. Kevin From mboxrd@z Thu Jan 1 00:00:00 1970 From: khilman@kernel.org (Kevin Hilman) Date: Wed, 10 Jun 2015 10:01:10 -0700 Subject: [PATCH RFC 3/3] PM / Domains: Introduce generic PM domain for cpu domain In-Reply-To: <5574121F.2000806@samsung.com> (Krzysztof Kozlowski's message of "Sun, 07 Jun 2015 18:42:55 +0900") References: <1433456946-53296-1-git-send-email-lina.iyer@linaro.org> <1433456946-53296-4-git-send-email-lina.iyer@linaro.org> <5574121F.2000806@samsung.com> Message-ID: <7hbngnpkfd.fsf@deeprootsystems.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Krzysztof Kozlowski writes: > W dniu 05.06.2015 o 07:29, Lina Iyer pisze: >> Generally cpus are grouped under a power domain in a SoC. When all cpus >> in the domain are in their power off state, > > What do you exactly mean here by "CPU in power off state"? How does it > map to kernel understanding of CPU device (hotplug? cpuidle?)? > >> the cpu domain can also be >> powered off. Genpd provides the framework for defining cpus as devices >> that are part of a cpu domain. > > The problem which is solved looks to me like the same problem which > coupled cpuidle tried to solve: a certain deep sleep mode (e.g. power > off) can be entered when whole cluster is idle or other CPUs in cluster > are powered off completely. > > It seems a little like duplicating the effort around coupled cpuidle. Yes, it duplicates some aspects of coupled idle states, but coupled states have their own limitations: - only handles CPUs, not other devices sharing a power rail (e.g. L2$, GIC, floating point unit, CoreSight, etc. etc.) - not scaling well past 2 CPUs - doesn't handle clusters: While this series only addresses CPUs currently, the approach can be extended. Because genpd handles nested domains, the could be used to model clusters as well. Kevin