Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263042AbUJ1NGr (ORCPT ); Thu, 28 Oct 2004 09:06:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263055AbUJ1NGp (ORCPT ); Thu, 28 Oct 2004 09:06:45 -0400 Received: from mail.timesys.com ([65.117.135.102]:10342 "EHLO exchange.timesys.com") by vger.kernel.org with ESMTP id S263051AbUJ1NFd (ORCPT ); Thu, 28 Oct 2004 09:05:33 -0400 Message-ID: <4180EE56.4030100@timesys.com> Date: Thu, 28 Oct 2004 09:04:22 -0400 From: john cooper User-Agent: Mozilla Thunderbird 0.8 (X11/20040913) X-Accept-Language: en-us, en MIME-Version: 1.0 To: karim@opersys.com CC: Andrew Morton , paulmck@us.ibm.com, linux-kernel@vger.kernel.org, mingo@elte.hu, rpm@xenomai.org, john cooper Subject: Re: [RFC][PATCH] Restricted hard realtime References: <20041023194721.GB1268@us.ibm.com> <417F12F1.5010804@opersys.com> <20041026212956.4729ce98.akpm@osdl.org> <4180DDFA.1050409@opersys.com> In-Reply-To: <4180DDFA.1050409@opersys.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 28 Oct 2004 13:00:08.0406 (UTC) FILETIME=[0D44AF60:01C4BCEE] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1491 Lines: 37 Karim Yaghmour wrote: > Usually one of the litmus tests for this is to hook a function > generator to the system and inject a square wave through an > interrupt-generating I/O (ex.: parallel port), while measuring the > response time of an interrupt service routine and comparing it to > the input wave using an oscilloscope. One sign that the system is > indeed deterministic is that both square waves should appear > steady regardless of the load. Ideally yes, but there will still be some phase modulation due to the natural randomness of interrupt masking for hard irqs and from scheduling preemption latency for irqs run in task context. Also contributing to this will be latency due to interrupt hardware which may not be constant. One likely observation will be increased contention from periodic interrupt sources (clock) with the injected square wave interrupt when these frequencies (or their harmonics) approach each other. The contention would appear periodic at the difference of these interrupt frequencies. Other sources of phase bobble will include variable CPU cache content, loading of the bus from other DMA masters, SMP bus contention, etc.. which are much more difficult to address. -john -- john.cooper@timesys.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/