From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267400AbUHSU7Q (ORCPT ); Thu, 19 Aug 2004 16:59:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267398AbUHSU47 (ORCPT ); Thu, 19 Aug 2004 16:56:59 -0400 Received: from e6.ny.us.ibm.com ([32.97.182.106]:37615 "EHLO e6.ny.us.ibm.com") by vger.kernel.org with ESMTP id S267401AbUHSU4I (ORCPT ); Thu, 19 Aug 2004 16:56:08 -0400 Subject: Re: System time slowdown after upgrading from 2.4 to 2.6 From: john stultz To: ivan.kalatchev@esg.ca Cc: lkml In-Reply-To: <000501c48624$b1ac72f0$2e646434@ivans> References: <000501c48624$b1ac72f0$2e646434@ivans> Content-Type: text/plain Message-Id: <1092949099.2429.427.camel@cog.beaverton.ibm.com> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.5 (1.4.5-7) Date: Thu, 19 Aug 2004 13:58:19 -0700 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2004-08-19 at 12:42, Ivan Kalatchev wrote: > We have a project that uses PC-104 (ZFx86 100 MHz CPU) Linux box to acquire > some seismological signals. System resides on a M-Systems DiskOnChip 2000. > We have an ISA acquisition card that acquires data into FIFO buffer and > triggers interrupt as soon as 341 points were acquired (then this data is > read out in interrupt handler routine). System worked perfectly well when we > used 2.4.18 kernel. When I printk-ed system time (do_gettimeofday) in > interrupt routine, at 1kHz sampling frequency interrupts were reported every > 341 msec as they should do. > But after I've switched to 2.6 kernel (2.6.7 - preempted, then I tried > 2.6.8 - non-preempted) time between successive interrupts at 1kHz became 335 > msec, losing 6 msec at each interrupt. What is interesting, when sampling > frequency is 10 kHz, with 2.4.18 kernel interrupts are reported every 34 > msec, which is right, but with 2.6 kernels interrupts are coming at 28 msec > interval, again losing same 6 msec! > > Any ideas why this might happen? Hmm. Strange. Just to remove some variables, are you running NTP on the system? Could you also send your 2.6 dmesg? thanks -john