From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gilles Chanteperdrix Subject: Re: cyclictest better values with system load than without (OMAP3530 target) Date: Fri, 29 Nov 2013 17:36:34 +0100 Message-ID: <5298C292.2030502@xenomai.org> References: <5294681E.10406@gmail.com> <20131126101232.21636c8f@sluggy> <20131129125623.GB31099@linutronix.de> <5298AE4B.7070806@osadl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Sebastian Andrzej Siewior , Clark Williams , Stefan Roese , linux-rt-users@vger.kernel.org To: Carsten Emde Return-path: Received: from sd-51317.dedibox.fr ([62.210.215.82]:56243 "EHLO sd-51317.dedibox.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754121Ab3K2QxT (ORCPT ); Fri, 29 Nov 2013 11:53:19 -0500 In-Reply-To: <5298AE4B.7070806@osadl.org> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On 11/29/2013 04:10 PM, Carsten Emde wrote: > BTW: Power saving and real-time do not necessarily exclude each other. > If a - still deterministic - but a little longer latency is acceptable, > some light sleep states and a somewhat lower clock frequency may be > allowed which still may result in considerable energy saving. If, > however, the fastest possible real-time response is required, C states > and P states must be disabled (or set to polling and maximum speed, > repsectively) and the power bill must be payed. Well, I do not fully agree. To be sure that you can clock down the processor for executing a task which has sufficient time to meet its deadline, your system must be "time triggered", all the timer events must be known in advance. Because on a fully dynamic system, you may make that decision, but a new timer may be scheduled which causes the system to miss its deadline whereas it would not have missed it if it had run at full speed. -- Gilles.