Date: Thu, 17 Jul 1997 11:36:57 +0800 From: Peter Wemm <peter@spinner.dialix.com.au> To: listuser <listuser@h2o.journey.net> Cc: Chuck Robey <chuckr@Glue.umd.edu>, Steve Passe <smp@csn.net>, smp@FreeBSD.ORG Subject: Re: HEADS UP: EISA cards. Message-ID: <199707170336.LAA23469@spinner.dialix.com.au> In-Reply-To: Your message of "Wed, 16 Jul 1997 23:10:16 -0400." <Pine.BSF.3.95q.970716230927.6743A-100000@h2o.journey.net>
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listuser wrote:
> Just an FYI DELL computer still sells their SMP servers with 3 PCI and 5
> EISA slots ...
> (Or at least two months ago when I bought one from them..)
>
> --Matt
Again, remember that the feature that we are talking about (DMA Chaining)
is *not* implemented in the uniprocessor kernel either! I do not know of
*any* devices that use it. All the EISA DMA devices that I know of (eg:
AHA 1742, 2742, BusLogic etc controllers) use Busmaster DMA, not the lame
64K-at-a-time DMA chunking driven by the motherboard DMA counters. The DMA
Chaining interrupt is (I think) used to try and work around of that
lameness. In fact, the only devices that I can think of that use the
motherboard DMA counters are ISA soundcards and the floppy controller. I
can't recall ever seeing an EISA soundblaster clone type card. Most decent
(if you can call it that) ISA hardware that uses DMA does busmastering too
(eg: the adaptec scsi host adapters).
What we are talking about is making a design choice that will prevent us
from implementing DMA chaining in the future. I think the possibility of
needing to do that that is exceedingly unlikely. And I would argue that
doing that sort of non-busmastering DMA would be kind of defeating the
purpose of building a high performance system with multiple CPUs anyway.
Cheers,
-Peter
> On Wed, 16 Jul 1997, Chuck Robey wrote:
>
> > On Tue, 15 Jul 1997, Steve Passe wrote:
> >
> > > Hi,
> > >
> > > DESIGN DECISION:
> > >
> > > I am about to make a design decision that will forever-more make the use
> > > of EISA cards that use the EISA chipset DMA circuit impossible in the SMP
> > > kernel. I posted a rather long email about this several days ago but got
ZERO
> > > response. So I can conclude that either:
> > >
> > > a: everyone agrees with this decision.
> > > OR
> > > b: no one with such hardware read that far.
> > >
> > > In the future I will use this "HEADS UP" format to get a summary of such
> > > info to the top of email. For the record, here is a repost of the
> > > pertinant info:
> >
> > Steve, I don't have an EISA smp board, so I felt I didn't need to reply,
> > but your suggestion is fine with me. Thinking about it, the only EISA
> > boards out there would be getting a little aged, and it seems fairly safe
> > to exclude them from smp work.
> >
> > ----------------------------+----------------------------------------------
-
> > Chuck Robey | Interests include any kind of voice or data
> > chuckr@eng.umd.edu | communications topic, C programming, and Unix
.
> > 213 Lakeside Drive Apt T-1 |
> > Greenbelt, MD 20770 | I run Journey2 and picnic, both FreeBSD
> > (301) 220-2114 | version 3.0 current -- and great FUN!
> > ----------------------------+----------------------------------------------
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