Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 20 Dec 2002 19:41:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 20 Dec 2002 19:41:25 -0500 Received: from sabre.velocet.net ([216.138.209.205]:5636 "HELO sabre.velocet.net") by vger.kernel.org with SMTP id ; Fri, 20 Dec 2002 19:41:25 -0500 To: linux-kernel@vger.kernel.org Subject: Problem with read blocking for a long time on /dev/scd1 From: Gregory Stark Date: 20 Dec 2002 19:49:28 -0500 Message-ID: <87adj0b3hj.fsf@stark.dyndns.tv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1993 Lines: 39 I'm having a problem with ogle that seems to be being caused by the scsi or ide-scsi driver. The video playback freezes for a second or randomly, sometimes every few seconds, sometimes not for several minutes. Every such glitch is correlated perfectly with a read syscall reading on /dev/scd1 blocking for an inordinate amount of time. Most read syscalls from ogle seem to take between 30us to 100ms depending on the size of the read. In fact plotting the time taken reported by strace -T vs the size of the read in gnuplot produces a nice obvious linear correlation. However occasionally there are outlier samples where the read call blocks for between 150ms up to 1s or more. I've seen it block for about 10s once. I've tried this on a machine that was essentially in single-user mode. The only processes running were X, ogle, an xterm, and not much else. I'll include my normal lsmod output below but the problem still occurred when playing with hardly any modules loaded. There's an FAQ about ogle glitching like this when something tries to probe the cd drive, but nothing like that is running. And the glitches aren't periodic like that FAQ describes. The problem is definitely that the kernel simply doesn't schedule the process calling read for over a second. There are no dmesg messages or other indication of problems in the ide-scsi or scsi drivers. Where would I start to track down what is preventing the kernel from scheduling this process? It's presumably some problem in the ide or ide-scsi driver, but I'm not sure where to start. [I'm having trouble sending messages to the list, my ISPs mail server didn't seem to deliver it the first time. My apologies if it finally makes it through and this is a duplicate] -- greg - 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/