From owner-freebsd-hackers Wed Jul 4 20:12:43 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from panzer.kdm.org (panzer.kdm.org [216.160.178.169]) by hub.freebsd.org (Postfix) with ESMTP id 4F1EB37B403; Wed, 4 Jul 2001 20:12:38 -0700 (PDT) (envelope-from ken@panzer.kdm.org) Received: (from ken@localhost) by panzer.kdm.org (8.9.3/8.9.1) id VAA48163; Wed, 4 Jul 2001 21:12:33 -0600 (MDT) (envelope-from ken) Date: Wed, 4 Jul 2001 21:12:33 -0600 From: "Kenneth D. Merry" To: Kevin Hui Cc: freebsd-questions@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG Subject: Re: Raw disk access in userland Message-ID: <20010704211233.A48146@panzer.kdm.org> References: <20010704170844.A47113@panzer.kdm.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2i In-Reply-To: ; from khui@cs.toronto.edu on Wed, Jul 04, 2001 at 08:18:51PM -0400 Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Wed, Jul 04, 2001 at 20:18:51 -0400, Kevin Hui wrote: > Then the question is whether the kernel is copying data between userspace > and kernelspace or whether it just DMAs the data straight in/out of the > user program's address space. In Linux raw-io, given that it is a block > device and you are doing page-aligned block I/Os on it, is smart and does > zero copies. While it may seem to be jumping through hoops, maybe it does > have a performance advantage? The kernel copies between userland and the kernel. Ken -- Kenneth Merry ken@kdm.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message