Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965087AbXAYMEI (ORCPT ); Thu, 25 Jan 2007 07:04:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932936AbXAYMEI (ORCPT ); Thu, 25 Jan 2007 07:04:08 -0500 Received: from smtp5-g19.free.fr ([212.27.42.35]:48375 "EHLO smtp5-g19.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932886AbXAYMEH (ORCPT ); Thu, 25 Jan 2007 07:04:07 -0500 X-Greylist: delayed 7315 seconds by postgrey-1.27 at vger.kernel.org; Thu, 25 Jan 2007 07:04:07 EST Message-ID: <45B89C99.2060500@free.fr> Date: Thu, 25 Jan 2007 13:03:37 +0100 From: John User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.8) Gecko/20061108 SeaMonkey/1.0.6 MIME-Version: 1.0 To: linux-kernel@vger.kernel.org CC: tglx@timesys.com, mingo@elte.hu, johnstul@us.ibm.com, akpm@osdl.org, shill@free.fr Subject: Re: One-shot high-resolution POSIX timer periodically late References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1952 Lines: 59 [ Re-sending in the hope that it will be archived ] Ingo Molnar wrote: > John Stultz wrote: > >> On Wed, 2007-01-24 at 10:41 +0100, John wrote: >> >>> I'm using the POSIX timers API. My platform is x86 running Linux >>> 2.6.18.6 patched with the high-resolution timer subsystem. >>> >>> http://www.tglx.de/hrtimers.html >>> >>> My process is the only SCHED_FIFO process on the system. There are >>> no user-space processes with a higher priority. AFAICT, only a >>> kernel thread could keep the CPU away from my app. >>> >>> Is there a periodic kernel thread that runs every 2 seconds, cannot >>> be preempted, and runs for over 50 ?s?? >> >> This sounds like a BIOS SMI issue. Can you reproduce this behavior on >> different hardware? > > note that only the -hrt patchset is used - not the full -rt patchset > - so 50 usecs delays (and more) are quite possible and common. Ingo, You are correct, I only used -hrt. I will _definitely_ give -rt a try. I am fully aware that an occasional 100 ?s delay is possible, given a soft real-time operating system. However, what I cannot explain is: Why do these /occasional/ delays always happen a multiple of 2 seconds apart? Can you explain this odd behavior? > My question would be: does the same problem occur with the full -rt > patchset and PREEMPT_RT? (see http://rt.wiki.kernel.org for details) I will test on a different PC, as John suggested. I will try the full -rt patchset in a few days. +++++ On a related note, there is no -hrt patch for 2.6.19: http://www.tglx.de/projects/hrtimers/ Is it because the patch for 2.6.19-rc4-mm1 applies cleanly to 2.6.19? There is no -hrt patch for 2.6.20. Has it been completely merged? Regards. - 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/