Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!ll-xn!cit-vax!mangler From: mangler@cit-vax.Caltech.Edu (System Mangler) Newsgroups: comp.unix.wizards Subject: Re: BSD 4.2 minphys() < 64K Message-ID: <1361@cit-vax.Caltech.Edu> Date: Wed, 17-Dec-86 17:42:06 EST Article-I.D.: cit-vax.1361 Posted: Wed Dec 17 17:42:06 1986 Date-Received: Thu, 18-Dec-86 03:59:30 EST References: <376@wyszecki.munsell.UUCP> <1871@utah-gr.UUCP> <4763@mimsy.UUCP> Organization: California Institute of Technology Lines: 30 Summary: Two 16-bit MBA byte counts in one 32-bit register In article <376@wyszecki.munsell.UUCP>, jwf@munsell.UUCP (Jim Franklin) writes: > I would like to be able to blast a 1/4 megabyte to a disk in one i/o -- > the disk, disk controller, and device driver can all deal with this. What kind of disk controller? In article <4763@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes: > The MBA byte count register is 32 bits wide, The MBA byte count register contains two 16-bit byte counts: the number of bytes transferred to/from memory, and the number transferred to/from the drive. On an error, they may differ, due to buffering. The 16-bit byte counts limit the MBA to at most 127 sectors at a time. The massbus disk driver really ought to supply its own minphys to deal with 516 byte sectors (which happen when you're writing the headers). > At 63k-at-a-time, I get a raw data rate of > 1.1Mb/s on a Vax 785 with Eagles on an Emulex SC788 Even a lowly 750 can do that, given Eagles. > This amounts to less than 20 interrupts per second---quite trivial; Lost revolutions, not interrupts, are the issue, and only when you're doing fairly specialized things, like a database writing raw cylinders, fast bad-block checking, or image backup to a 200-ips 6250-bpi streamer, all of which probably require more CPU horsepower than a VAX anyway. Don Speck speck@vlsi.caltech.edu {seismo,rutgers,ames}!cit-vax!speck