From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1IpWYH-0006pe-U6 for qemu-devel@nongnu.org; Tue, 06 Nov 2007 17:05:42 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1IpWYG-0006lq-AV for qemu-devel@nongnu.org; Tue, 06 Nov 2007 17:05:41 -0500 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1IpWYG-0006lK-43 for qemu-devel@nongnu.org; Tue, 06 Nov 2007 17:05:40 -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 1IpWYF-0002c4-G8 for qemu-devel@nongnu.org; Tue, 06 Nov 2007 17:05:39 -0500 From: Paul Brook Subject: Re: [Qemu-devel] RFC: x86_64 Best way to fix 'cast to pointer from integer of different size' problems? Date: Tue, 6 Nov 2007 22:05:34 +0000 References: <1194110810.13889.25.camel@hephaestion> <4730C8EC.8030808@bellard.org> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200711062205.34944.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: Stuart Anderson > By the time you consider the different combinations of targets & hosts, > most of the opportunities for zero copy are eliminated anyway. Byte > ordering and structure packing amd content differences mean that we can't > do zero-copy except in the rare circumstance that the host & target > match is all of these respects. The read & write buffers would still > benefit from zero copy, but nearly everything else has to be touched > anyway. If you're not careful you get double-copying. Once copying the struct from guest to host space, and then again when converting layout/endianess. I've no idea whether this overhead is important in practice though. Paul