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From: terry@cs.weber.edu (A Wizard of Earth C)
Subject: Re: [386BSD] What SCSI controllers _are_ supported?
Message-ID: <1993Feb17.214948.9390@fcom.cc.utah.edu>
Keywords: 386BSD SCSI
Sender: news@fcom.cc.utah.edu
Organization: Weber State University (Ogden, UT)
References: <QJufrAlBBh107h@hansford.com> <C2LoMH.46p@cs.mcgill.ca> <C2Luz6.1CzA@austin.ibm.com>
Date: Wed, 17 Feb 93 21:49:48 GMT
Lines: 65
In article <C2Luz6.1CzA@austin.ibm.com> guyd@austin.ibm.com (Guy Dawson) writes:
>
>In article <C2LoMH.46p@cs.mcgill.ca>, storm@cs.mcgill.ca (Marc Wandschneider) writes:
>> In article <QJufrAlBBh107h@hansford.com> murrayc@hansford.com (Charles H. Murray) writes:
>> >In <count.729725567@mits> count@mits.mdata.fi (Bror Heinola) writes:
>> >> I'll be transferring a 386BSD system to SCSI from WD1007 ESDI and
>> >> I'd like to know what controllers are supported
>> >> a) in kernel
>> >> b) with special add-on drivers
>> >
>> >What about support for the Ultrastor 34F, VESA Local Bus SCSI-2 bus
>> >mastering controller. I would love to see the performance of 386BSD
>> >with this card.
>>
>> You left out a few buzzwords, like super-duper superscalar multi-
>> segmented ultra buffering caching controller.
>>
>> Boy, would marketing be upset.
>
>At the risk of starting another Flame Fest(tm), who beleives that a
>caching controller will improve performance much ( say 5% ) over the
>caching that BSD does?
If the controller can be accessed as fast as local memory, then yes, a
caching controller will help above and beyond the caching done by 386BSD.
The reasoning is that it's nearly always faster to hit memory locally
than it is to hit memory on a card over a bus, and the caching done on the
card, if it's optimized at all, is optimized for the way DOS accesses hard
drives.
You may see some slight improvement on sequential reads; on the other hand,
Julians driver supports sufficiant optimizations in the way controllers are
used to make predictive read-ahead on a cached SCSI controller almost a 0
win.
You may also see a read performance increase due to hiding of the
cylinder boundries by the caching (probably the best place for a cache on
a controller to help you out, especially with a translated drive). To
take advantage of this, you would have to disable some of the block I/O
optimizations that try to compensate for cylinder boundries (as they would
now tend to slow you down).
A cached controller can, depending on the caching done, prevent important
changes from hitting the disk (if it's write caching). In any case, LRU
invalidation will only speed up the initial period of a high-use cycle
(such as a compile), after which the buffers will saturate, and any write
caching will perform like write-through anyway.
The biggest DOS performance gain, prereading and caching .EXE files on the
initial ready assuming that the entire file will be read, won't help in
386BSD, since the entrie image is not loaded at the same time. The pages
are allocated, but they are marked fill-from-file.
Terry Lambert
terry@icarus.weber.edu
terry_lambert@novell.com
---
Any opinions in this posting are my own and not those of my present
or previous employers.
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