From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752027AbXAXULI (ORCPT ); Wed, 24 Jan 2007 15:11:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752066AbXAXULI (ORCPT ); Wed, 24 Jan 2007 15:11:08 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:36604 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752027AbXAXULF (ORCPT ); Wed, 24 Jan 2007 15:11:05 -0500 Date: Wed, 24 Jan 2007 21:09:47 +0100 From: Ingo Molnar To: john stultz Cc: John , linux-kernel@vger.kernel.org, tglx@timesys.com, akpm@osdl.org, shill@free.fr Subject: Re: One-shot high-resolution POSIX timer periodically late Message-ID: <20070124200947.GA925@elte.hu> References: <45B729AF.4030701@privacy.net> <1169665347.6905.3.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1169665347.6905.3.camel@localhost.localdomain> User-Agent: Mutt/1.4.2.2i X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -4.3 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-4.3 required=5.9 tests=ALL_TRUSTED,BAYES_00 autolearn=no SpamAssassin version=3.0.3 -3.3 ALL_TRUSTED Did not pass through any untrusted hosts -1.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0009] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * 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 µs?? > > 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. 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) Ingo