Date: Sat, 19 Apr 1997 07:07:40 -0400 (EDT) From: Peter Dufault <dufault@hda.com> To: hasty@rah.star-gate.com (Amancio Hasty) Cc: hackers@freebsd.org Subject: Re: video capture driver interface to file system? Message-ID: <199704191107.HAA21112@hda.hda.com> In-Reply-To: <199704181915.MAA06203@rah.star-gate.com> from Amancio Hasty at "Apr 18, 97 12:15:58 pm"
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> I get : > time dd if=/dev/zero of=/spare/test bs=3456000 count=30 > 30+0 records in > 30+0 records out > 103680000 bytes transferred in 36.080174 secs (2873600 bytes/sec) > 0.000u 5.297s 0:37.18 14.2% 78+9000k 8+1641io 6pf+0w > The partition is on a > sd0: <SEAGATE ST15150W 0023> type 0 fixed SCSI 2 > and the adapter is a 2940w. Well, that eliminates the simplest approach of through the file system on your system. I'd still do that first as a base line since it will make it easy to debug the driver. I read Mike Smith's suggestions. I have another which I'd look at before doing file I/O inside the kernel - that is only covering up the context switch time, and I find it hard to accept that that is going to make or break the application. How about: 1. Driver mmap of buffers into the process address space; 2. An rtprio user process; 3. A synchronization token that can be read back saying which buffer was loaded; 4. Raw I/O to a partition and your own clip storage management. This will eliminate the copies and if it can be done at all I bet it can be done this way. You may want to time your double buffered raw I/O throughput and see if you're going to be able to do this with your hardware. After this is working you could start considering raw I/O to a file system partition using pre-allocated files if needed - I'd still do this part first. I've been adding the POSIX 4 interface, and John Dyson is working on async I/O. The async I/O will make the data logger a bit more straight forward - you'll have a few transfers out there and handle the pending / completion handling in a standard way. -- Peter Dufault (dufault@hda.com) Realtime Machine Control and Simulation HD Associates, Inc. Voice: 508 433 6936
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