Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261678AbVEZST7 (ORCPT ); Thu, 26 May 2005 14:19:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261682AbVEZST7 (ORCPT ); Thu, 26 May 2005 14:19:59 -0400 Received: from viper.oldcity.dca.net ([216.158.38.4]:7121 "HELO viper.oldcity.dca.net") by vger.kernel.org with SMTP id S261678AbVEZSTb (ORCPT ); Thu, 26 May 2005 14:19:31 -0400 Subject: Re: 2.6.11 timeval_to_jiffies() wrong for ms resolution timers From: Lee Revell To: linux-os@analogic.com Cc: Olivier Croquette , LKML , george@mvista.com In-Reply-To: References: <21FFE0795C0F654FAD783094A9AE1DFC07AFE7C1@cof110avexu4.global.avaya.com> <4294D9C6.3060501@mvista.com> <4296019B.8070006@free.fr> Content-Type: text/plain Date: Thu, 26 May 2005 14:19:27 -0400 Message-Id: <1117131568.5477.12.camel@mindpipe> Mime-Version: 1.0 X-Mailer: Evolution 2.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1382 Lines: 30 On Thu, 2005-05-26 at 14:10 -0400, Richard B. Johnson wrote: > The time for a sleeping (waiting) task to get the CPU is much > greater than the jitter. Once in the ISR, some wake-up call > is "scheduled" and the interrupt returns. A CPU hog may have > been using the CPU when the interrupt occurred. It will continue > to use the CPU until its time-slot (quantum) has expired. This > could be a whole millisecond if HZ is 1000, 10 milliseconds if > 100. It's only then that your sleeping task gets awakened > by the interrupting event. > > So, accurate waking up is not guaranteed on any multi-user, > multitasking system because you don't know what a user has > been doing with the CPU. On a dedicated machine, one can > have tasks that are most always sleeping or waiting for > I/O so, the latency can come way down. However, signaling > a task, based upon some time will never be very accurate > anywhere. Not quite, if your sleeping task has higher priority than the CPU hog it will preempt the CPU hog immediately on return from the interrupt. Unless you've disabled preemption of course, which would be stupid in this case. Lee - 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/