From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755630AbZKBP4F (ORCPT ); Mon, 2 Nov 2009 10:56:05 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755379AbZKBP4F (ORCPT ); Mon, 2 Nov 2009 10:56:05 -0500 Received: from mail.gmx.net ([213.165.64.20]:36182 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1755333AbZKBP4D (ORCPT ); Mon, 2 Nov 2009 10:56:03 -0500 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1+K2slxbRSKrvkMVZKY9j8/2VYvdET3y0vyzuCEr1 rZ3bdFhqMXl3nI Subject: Re: [Bug 12309] Large I/O operations result in slow performance and high iowait times From: Mike Galbraith To: Thomas Pilarski Cc: Ingo Molnar , Peter Zijlstra , Andrew Morton , LKML In-Reply-To: <20091101134207.b97e4f5f.akpm@linux-foundation.org> References: <20091101134207.b97e4f5f.akpm@linux-foundation.org> Content-Type: text/plain Date: Mon, 02 Nov 2009 16:56:04 +0100 Message-Id: <1257177364.10173.23.camel@marge.simson.net> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1.1 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 X-FuHaFi: 0.57 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > --- Comment #412 from Thomas Pilarski 2009-11-01 21:28:24 --- > Created an attachment (id=23618) > --> (http://bugzilla.kernel.org/attachment.cgi?id=23618) > Simple sleeper test case > > As this bug occurs more permanent while working in an virtual machine or while > using java and I still think, that's this is a process scheduler bug (or > something related). Here another test case, which shows the suspected > behaviour. As there are many system calls while using a virtual machine, I have > tries to find an equal test. The test case just sleeps for 1__s and measures the > time difference of the usleep operation. I am using such many of the usleep > operations, as the problems does not occur deterministic and I tried to catch > as many as possibly occurrences. > > I have run this test case on three machines. The first one was a Core2 Duo with > a first generation SDD (OCZ Core Series) with a poor write performance and on a > Ubuntu kernel 2.6.31-14-generic. The partitions are block aligned. I have run > this test, while my wife was using firefox. Every time, she was submitting > something and firefox is using sqlite for writing the history, there was a high > latency for the sleep test. > > Timediff 7629094: 16.80ms Total: 61.12ms > Timediff 7629100: 18.82ms Total: 93.68ms > Timediff 7629101: 19.96ms Total: 113.54ms > Timediff 7629102: 19.98ms Total: 133.43ms > Timediff 7629103: 19.97ms Total: 153.31ms > Timediff 7629104: 20.00ms Total: 173.24ms > Timediff 7629105: 19.96ms Total: 193.09ms > Timediff 7629106: 20.02ms Total: 213.02ms > Timediff 7629107: 19.94ms Total: 232.86ms > Timediff 7636162: 16.40ms Total: 34.44ms > Timediff 7636164: 19.90ms Total: 64.00ms > > While the duration of 100 usleep should be somewhere between 10ms and 20ms, 10 > usleep(1) takes more than 200ms. This behaviour is reproducible. Can you please try the latest -rc? I spent the day trying to coax a latency spike out of -tip, including thumping disk with dd, mysql+oltp rw test et al, and failed. -Mike