[info] [Beowulf] 64-core processor...

[Eugen Leitl]

----- Forwarded message from Mark Hahn <hahn at mcmaster.ca> -----

From: Mark Hahn <hahn at mcmaster.ca>
Date: Tue, 21 Aug 2007 15:09:57 -0400 (EDT)
To: Larry Stewart <larry.stewart at sicortex.com>
Cc: "beowulf at beowulf.org" <Beowulf at beowulf.org>
Subject: Re: [Beowulf] 64-core processor...


I googled on "+raw +multicore +mesh", and found, among other things, 
a book chapter that went into some detail on the "Raw" prototype:

http://www.springerlink.com/index/g3u708645278lv32.pdf

(access might be limited to campuses that have agreements w/springer.)

I'm guessing that Tilera is a lot like Raw - couple generations more 
agressive fab, probably cleaned up design, etc.  here's the Tilera guy
talking about tiled multicore streaming architectures:

http://videos.dac.com/44th/slides/42_2.ppt

>From the picture in Ars Technica, there are four memory controllers for 64 
>processors. There is no floating point, but there would certainly be room 
>for it in a 65 nm version.

I'm pretty sure Raw had FP, and guess Tilera does as well (not DP though.)

>It seems to me that the key difficulty for building larger clusters out of 
>these things
>is the imbalance between computing and memory bandwidth.

well, I think the premise of most massively multicore is a 
dataflow/streaming design for programs, not a memory-based model.  more 
recv-compute-send
rather than load-compute-store.

one very frustrating thing about Tilera is the total vapidity of their 
published docs.  for instance, inter-tile latency, which is pretty critical
in evaluating how much cache misses will hurt.  heck, I'm not even clear 
about whether the caches implement coherency, or whether they're sw-managed.

>and routing, but not so fine for general purpose computing.  16 cores per 
>DDR interface
>(doesn't say if they are 64 or 128 bits wide, but I would guess 64 based on 
>reasonable size
>package pin counts) seems way too skinny a pipe to memory to be reasonable.

four DDR interfaces, which I also would guess would be a dimm wide (64b),
or something like 40 GB/s.  that really doesn't seem too terribly shabby ;)

I would be most interested in a detailed comparison of your chip, Tilera's
and just for amusement, Sun's new one ;)

regards, mark hahn.
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