From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Gleixner Subject: Re: [PATCH v2 7/7] ARM: smp: Add runtime PM support for CPU hotplug Date: Tue, 22 Sep 2015 22:53:14 +0200 (CEST) Message-ID: References: <2657565.lxWtPmdjyp@vostro.rjw.lan> <55ED9328.2010501@ti.com> <2355864.I8qZFusWfm@vostro.rjw.lan> <55EE9AA1.8020200@ti.com> <7h613kmuuv.fsf@deeprootsystems.com> <55F162FD.4050401@ti.com> <20150922173236.GB19183@linaro.org> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Return-path: Received: from www.linutronix.de ([62.245.132.108]:43200 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933703AbbIVUx7 (ORCPT ); Tue, 22 Sep 2015 16:53:59 -0400 In-Reply-To: <20150922173236.GB19183@linaro.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Lina Iyer Cc: Grygorii Strashko , Kevin Hilman , "Rafael J. Wysocki" , Alan Stern , Russell King - ARM Linux , Mark Rutland , ulf.hansson@linaro.org, Lorenzo Pieralisi , linux-pm@vger.kernel.org, Catalin Marinas , k.kozlowski@samsung.com, msivasub@codeaurora.org, geert@linux-m68k.org, agross@codeaurora.org, sboyd@codeaurora.org, linux-arm-kernel@lists.infradead.org, Ingo Molnar , john.stultz@linaro.org On Tue, 22 Sep 2015, Lina Iyer wrote: > Talking to John Stultz at Linaro Connect: Is cpuidle relevant in > -RT kernel? I dont know much about -RT. I thought this might be point > that we should consider. There are definitely RT systems out there where power consumption is a concern. > As it stands today, on a 800 Mhz ARM quad core, I am seeing a latency of > 50-70 usec for the additional runtime PM in the cpuidle. Ofcourse, there > is a definite need to optimize and there are opportunities to do that. RT is not about being fast. RT is about being deterministic. So if a power sensitive RT system can afford the extra latencies induced by PM it will tolerate them. Of course, optimizing that is not a bad thing at all :) Thanks, tglx