Return to BSD News archive
Path: sserve!newshost.anu.edu.au!harbinger.cc.monash.edu.au!bunyip.cc.uq.oz.au!munnari.oz.au!spool.mu.edu!howland.reston.ans.net!news.cac.psu.edu!news.pop.psu.edu!hudson.lm.com!godot.cc.duq.edu!ddsw1!not-for-mail From: chilton@MCS.COM (Christopher Hilton) Newsgroups: comp.os.386bsd.questions Subject: Re: Need HW/Drive purchase advice Date: 16 Mar 1995 09:16:12 -0600 Organization: /usr/lib/news/organi[sz]ation Lines: 52 Message-ID: <3k9kns$ibd@Mercury.mcs.com> References: <shamrock-1502952240270001@192.0.2.1> <3j3j5m$n70@helena.MT.net> <shamrock-0903951552350001@192.0.2.1> <3k167k$eb7@bonnie.tcd-dresden.de> NNTP-Posting-Host: mercury.mcs.com In article <3k167k$eb7@bonnie.tcd-dresden.de>, J Wunsch <joerg_wunsch@uriah.heep.sax.de> wrote: >Lucky Green <shamrock@netcom.com> wrote: > >[ISA bus-mastering DMA devices need bounce buffers with RAM > 16 MB] > >>I had just about decided on a Adapect 1542. But now I hear there might be >>problems using it on ISA with >16 MB. Do you think I'd better get a 1522? > >No. They are PIO (programmed I/O), just like an IDE, and hence they >will also hog the CPU as IDE drives do. No good decision for a multi- >processing o/s. The penalty for the bounce buffers (if you happen to >have > 16 MB) is much less. > >If you're buying a new machine and think about more than 16 MB RAM, do >also think about PCI and a PCI SCSI controller (e.g. NCR ...810), they >are rather cheap and do a good job -- and the bus doesn't suffer from >this ancient address space limit. > I second this. Bounce buffers are a cheap price to pay for the performance you get from bus mastering controllers. Are these PCI controllers bus-mastering? I've been looking into picking up an AVA-2822 as a stopgap until I can get a P90 or K5 with PCI. This is an AIC-6360 on a VLB card. E.g. a VLB 1522. The reports that I've seen say that it gets by the 3 MB/s limit of the ISA bus quite nicely. Performance of a Quantum Lightning 540S went from 2.8 MB/s to 5.2 MB/s just by changing the card. I understand intimately what you're saying about the AIC-6360 being a CPU hog in PIO mode. Way back when I wrote the scsi driver for Mark Williams Coherent. When I added code to chain multiple sequential requests into one SCSI request to the disk driver I tripled the throughput of the AHA-1542/Maxtor combo that I had. When I tried the same trick on the Seagate ST01 controller I only added 20 percent. The difference was that the Adaptec is "fire and forget". You put together a SCSI request and then the controller handles the rest. The Seagate however required hand-holding for each phase of the SCSI protocol. This left no cpu to queue and chain the requests so 4 times out of five the disk driver only saw one request at a time. C. -- Christopher Sean Hilton E-mail: chilton@mcs.com ---------------------------------------------------------------------- ICBM address: | "Thus it is said if you know them and know 42 07 39 N/87 49 44 W | yourself, your victory will not be imperiled. For PGP key finger: | If you know Heaven and you know Earth, your chilton@mcs.com | victory will be complete." - Sun Tsu ----------------------------------------------------------------------