From owner-freebsd-hackers Mon Apr 21 03:48:49 1997 Return-Path: Received: (from root@localhost) by freefall.freebsd.org (8.8.5/8.8.5) id DAA05197 for hackers-outgoing; Mon, 21 Apr 1997 03:48:49 -0700 (PDT) Received: from hda.hda.com (hda-bicnet.bicnet.net [207.198.1.121]) by freefall.freebsd.org (8.8.5/8.8.5) with ESMTP id DAA05190 for ; Mon, 21 Apr 1997 03:48:43 -0700 (PDT) Received: (from dufault@localhost) by hda.hda.com (8.8.5/8.8.5) id GAA24306; Mon, 21 Apr 1997 06:35:31 -0400 (EDT) From: Peter Dufault Message-Id: <199704211035.GAA24306@hda.hda.com> Subject: Re: video capture driver interface to file system? In-Reply-To: <199704210433.OAA07211@genesis.atrad.adelaide.edu.au> from Michael Smith at "Apr 21, 97 02:03:42 pm" To: msmith@atrad.adelaide.edu.au (Michael Smith) Date: Mon, 21 Apr 1997 06:35:30 -0400 (EDT) Cc: hasty@rah.star-gate.com, hackers@freebsd.org X-Mailer: ELM [version 2.4ME+ PL25 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-hackers@freebsd.org X-Loop: FreeBSD.org Precedence: bulk > I was actually believing that it would cover the uiomove() time as > well, which looked to be the worst offender. Some more study tells > me this was wrong, so yes, I'd have to agree that a user-space > application is probably going to perform nearly as well. I'm assuming DMA directly into the user buffer via physio for a raw transfer. I use "raw transfer" always to mean directly to user buffers. I guess I need to use "cooked" or "psuedo-raw" transfers to describe transfers that uiomove indirectly through kernel buffers. >From Amancio's brief description I assume the device is capable of DMAing to anywhere in PCI memory. The only cool optimization I can think of is to use non-ascending transfers to DMA directly to a SCSI controller's data FIFO ... but we'll talk about that when we're trying to do 40MB/second to a disk array. (I've done exactly that in an HDTV research application four years back, though it was only 20MB/sec). Peter -- Peter Dufault (dufault@hda.com) Realtime Machine Control and Simulation HD Associates, Inc. Voice: 508 433 6936