Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964885AbWEOLLb (ORCPT ); Mon, 15 May 2006 07:11:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964886AbWEOLLb (ORCPT ); Mon, 15 May 2006 07:11:31 -0400 Received: from ecfrec.frec.bull.fr ([129.183.4.8]:17288 "EHLO ecfrec.frec.bull.fr") by vger.kernel.org with ESMTP id S964885AbWEOLLa convert rfc822-to-8bit (ORCPT ); Mon, 15 May 2006 07:11:30 -0400 Subject: Re: rt20 scheduling latency testcase and failure data From: =?ISO-8859-1?Q?S=E9bastien_Dugu=E9?= To: Darren Hart Cc: lkml , Ingo Molnar , Thomas Gleixner , mista.tapas@gmx.net, efault@gmx.de, rostedt@goodmis.org, rlrevell@joe-job.com In-Reply-To: <200605121924.53917.dvhltc@us.ibm.com> References: <200605121924.53917.dvhltc@us.ibm.com> Date: Mon, 15 May 2006 13:15:46 +0200 Message-Id: <1147691746.3970.16.camel@frecb000686> Mime-Version: 1.0 X-Mailer: Evolution 2.4.2.1 X-MIMETrack: Itemize by SMTP Server on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 15/05/2006 13:14:28, Serialize by Router on ECN002/FR/BULL(Release 5.0.12 |February 13, 2003) at 15/05/2006 13:14:31, Serialize complete at 15/05/2006 13:14:31 Content-Transfer-Encoding: 8BIT Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1744 Lines: 39 On Fri, 2006-05-12 at 19:24 -0700, Darren Hart wrote: > I have been noticing unexpected intermittant large latencies. I wrote the > attached test case to try and capture some information on them. The librt.h > file contains convenience functions I use for writing other tests as well, so > much of it is irrelevant, but the test case itself is pretty clear I believe. > > The test case emulates a periodic thread that wakes up on time%PERIOD=0, so > rather than sleeping the same amount of time each round, it checks now > against the start of its next period and sleeps for that length of time. > Every so often it will miss it's period, I've captured that data and included > a few of the interesting bits below. The results are from a run with a > period of 5ms, although I have seen them with periods as high as 17ms. The > system was under heavy network load for some of the time, but not all. > Hi Darren, FWIW: I've been running you test program on my box under a stress-kernel load and did not observe any failure as you describe, not even a max latency overshooting the 100 us limit (max latencies in the 60~70 us). I even went to decrease PERIOD to 1 ms and still no failure. I'm running rt20 with the futex priority based wakeup patch on a dual 2.8 GHz HT Xeon box. All hardirq and softirq threads are at their default priority. How do you generate the network load you mention? Maybe I could try at least with the same load you're using. S?bastien. - 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/