Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751116AbWCYKDV (ORCPT ); Sat, 25 Mar 2006 05:03:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751129AbWCYKDV (ORCPT ); Sat, 25 Mar 2006 05:03:21 -0500 Received: from ozlabs.org ([203.10.76.45]:50581 "EHLO ozlabs.org") by vger.kernel.org with ESMTP id S1751116AbWCYKDU (ORCPT ); Sat, 25 Mar 2006 05:03:20 -0500 Subject: Re: [RFC PATCH 35/35] Add Xen virtual block device driver. From: Rusty Russell To: Alan Cox Cc: Jeff Garzik , Chris Wright , xen-devel@lists.xensource.com, SCSI Mailing List , Ian Pratt , virtualization@lists.osdl.org, ian.pratt@cl.cam.ac.uk, linux-kernel@vger.kernel.org In-Reply-To: <1143215728.18986.15.camel@localhost.localdomain> References: <4421D943.1090804@garzik.org> <1143202673.18986.5.camel@localhost.localdomain> <4423E853.1040707@garzik.org> <1143215728.18986.15.camel@localhost.localdomain> Content-Type: text/plain Date: Sat, 25 Mar 2006 21:03:11 +1100 Message-Id: <1143280992.8228.12.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.4.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1186 Lines: 28 On Fri, 2006-03-24 at 15:55 +0000, Alan Cox wrote: > On Gwe, 2006-03-24 at 07:38 -0500, Jeff Garzik wrote: > > > A pure SCSI abstraction doesn't allow for shared head scheduling which > > > you will need to scale Xen sanely on typical PC boxes. > > > > Not true at all. If you can do it with a block device, you can do it > > with a SCSI block device. > > I don't believe this is true. The complexity of expressing sequences of > command ordering between virtual machines acting in a co-operative but > secure manner isn't as far as I can see expressable sanely in SCSI TCQ I thought usb_scsi taught us that SCSI was overkill for a block abstraction? I have a much simpler Xen block-device implementation which seems to perform OK, and is a lot less LOC than the in-tree one, so I don't think the "SCSI would be better than what's there" (while possibly true) is valid. Cheers! Rusty. -- ccontrol: http://ozlabs.org/~rusty/ccontrol - 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/