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Date:      Mon, 20 Mar 95 10:35:36 MST
From:      terry@cs.weber.edu (Terry Lambert)
To:        rgrimes@gndrsh.aac.dev.com (Rodney W. Grimes)
Cc:        dufault@hda.com, hackers@freefall.cdrom.com
Subject:   Re: SMP work
Message-ID:  <9503201735.AA02256@cs.weber.edu>
In-Reply-To: <199503182206.OAA22038@gndrsh.aac.dev.com> from "Rodney W. Grimes" at Mar 18, 95 02:06:04 pm

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> I think that the locking model to be used should be discussed amongst
> us, as there are several alternatives.  I have no firm opinions on this
> issue.

There are two books I recommend for a discussion of the locking model:

UNIX Systems for Modern Architectures	-- Schimmel
The Magic Garden Explained

There's a third one coming out from Prentice Hall called (tentatively)
"UNIX Internals: The New Frontier".  I don't have a release date on
it yet.

> It wouldn't be SMP if they had separate buses now would it :-).  The
> ISA/EISA/PCI buses and cache and memory are shared by 2 CPU chips.

Actually, you can do loosely coupled SMP using a PCI/PCI bridge, per
the standards.  I don't know if anyone had built a board that could
handle this yet.

> These APIC's can be used for sending Interter Processor Interrupts,
> that is how you start the second CPU up.  They also allow you to control
> which CPU gets which interrupts.  You can prefer certain interrupts to
> certain CPU's or you can have it dispatch the interrupt to the lowest
> priority CPU, etc etc..  Since the APIC is built into the CPU the you
> don't have the high I/O latency of talking to things like 8259's to
> control them.

On the other hand, it's two bus cycles instead of one for a grant
with this type of arbitration.  On the third hand (8-).), single
cycle arbitration requires the use of ASICs that limit the number
of processers you can use without geometrically increasing the amount
of arbitration circuitry in your ASIC.

> There is a paper on the Intel MP spec on ftp.intel.com.  The file
> name is mpspec.ps, but I forget what directory it is in.

I have found this file to be corrupt.  Intel will mail you the spec
and it will only take a couple of days if you call their 800 number
for their doc department.  Or they may have fixed the file once I
reported it to their FTP person.


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



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