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Date:      Thu, 24 Jul 1997 13:57:17 -0700 (MST)
From:      Terry Lambert <terry@lambert.org>
To:        lamaster@george.arc.nasa.gov
Cc:        freebsd-smp@FreeBSD.ORG
Subject:   Re: Lots 'o PCI slots
Message-ID:  <199707242057.NAA18060@phaeton.artisoft.com>
In-Reply-To: <199707242002.NAA24606@george.arc.nasa.gov> from "lamaster@george.arc.nasa.gov" at Jul 24, 97 01:02:19 pm

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> That could be welcome news in some cases, but, since Unix/BSD folks
> tend to shy away from such boards anyway whenever possible, it seems
> that the only real "benefit" for well-behaved boards is going to be 
> increased latency.  For example, the most performance-critical
> path is usually the SCSI controller.  If the controller already
> has a minimal-interrupt message-passing flavor, does gather-scatter,
> etc., what's the difference?  Except for the added PCI bus traffic
> and the added latency due to the I/O request having to get processed
> in the I2O processor.
> 
> What am I missing?

PCI-PCI bridging, I would guess, where the i960 is a cluster
communications processor more than simply a method of offloading
interrupts.

It would be a relatively cheap method of obtaining background
distributed cache coherency processing (among other things).  One
might even use the i960 for the scheduler and for forcible process
migration.

Only a theory...


					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.



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