Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965085AbVINIb0 (ORCPT ); Wed, 14 Sep 2005 04:31:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965086AbVINIb0 (ORCPT ); Wed, 14 Sep 2005 04:31:26 -0400 Received: from smtp.osdl.org ([65.172.181.4]:24780 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S965085AbVINIb0 (ORCPT ); Wed, 14 Sep 2005 04:31:26 -0400 Date: Wed, 14 Sep 2005 01:30:53 -0700 From: Andrew Morton To: Mathieu Fluhr Cc: torvalds@osdl.org, linux-kernel@vger.kernel.org Subject: Re: 2.6.13 brings buffer underruns when recording DVDs in 16x (was Re: "Read my lips: no more merges" - aka Linux 2.6.14-rc1) Message-Id: <20050914013053.0c2b302c.akpm@osdl.org> In-Reply-To: <1126685479.2010.14.camel@localhost.localdomain> References: <1126608030.3455.23.camel@localhost.localdomain> <1126630878.2066.6.camel@localhost.localdomain> <1126635160.2183.6.camel@localhost.localdomain> <1126685479.2010.14.camel@localhost.localdomain> X-Mailer: Sylpheed version 1.0.4 (GTK+ 1.2.10; i386-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1234 Lines: 26 Mathieu Fluhr wrote: > > According to the MMC documentation, you can thoeriticaly send at most > 65535 (16 bits int) blocks in one WRITE(10) CDB. This would means > sending a buffer of ~127 MB on case of writing a mode 1 data track (2048 > bytes per block)... > > Now, practically, it is really not safe to send more than 64 KB per CDB > (Mostly device related). And with such values, you have the following: > - at 100 Hz -> 64 KB * 100 = 6400 KB/s <=> ~4.62x DVD > - at 250 Hz -> 64 KB * 250 = 16000 KB/s <=> ~11.55x DVD > - at 1000 Hz -> 64 KB * 1000 = 64000 KB/s <=> ~46.20x DVD But that implies that there's some piece of code somewhere (could be userspace, could be kernel) which is doing a timer-based sleep() in between each CDB. It shouldn't do that - it should be using the disk controller's completion interrupt for synchronisation. What userspace application are you using to write the DVDs, and is it possible to test a different one? - 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/