From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1IzEvL-0001po-PK for qemu-devel@nongnu.org; Mon, 03 Dec 2007 12:17:39 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1IzEvJ-0001np-NI for qemu-devel@nongnu.org; Mon, 03 Dec 2007 12:17:38 -0500 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1IzEvJ-0001nb-DD for qemu-devel@nongnu.org; Mon, 03 Dec 2007 12:17:37 -0500 Received: from mail.codesourcery.com ([65.74.133.4]) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1IzEvI-00025A-V9 for qemu-devel@nongnu.org; Mon, 03 Dec 2007 12:17:37 -0500 From: Paul Brook Subject: Re: [Qemu-devel] [PATCH 2/2 v2] Direct IDE I/O Date: Mon, 3 Dec 2007 17:17:23 +0000 References: <11966765602186@bull.net> <475426C7.20503@codemonkey.ws> <20071203170800.GC3797@implementation> In-Reply-To: <20071203170800.GC3797@implementation> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200712031717.24596.paul@codesourcery.com> Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Samuel Thibault On Monday 03 December 2007, Samuel Thibault wrote: > Anthony Liguori, le Mon 03 Dec 2007 09:54:47 -0600, a =E9crit : > > Have you done any performance testing? Buffered IO should absolutely > > beat direct IO simply because buffered IO allows writes to complete > > before they actually hit disk. > > Since qemu can use the aio interface, that shouldn't matter. Only if the emulated hardware and guest OS support multiple concurrent=20 commands. IDE supports async operation, but not concurrent commmands. In=20 practice this means you only get full performance if you're using the SCSI= =20 emulation. Paul