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[ars] Intel's Larrabee GPU based on secret Pentagon tech, sorta

post #1 of 6
Thread Starter 
Quote:

In a recent interview with German tech site heise.dk, Intel's Pat Gelsinger let slip some interesting information that I've been sitting on since last year, but haven't published: the processor cores that make up Intel's forthcoming Larrabee GPU are based on the original Pentium core design. Larrabee is, in essence, a bunch of P54C (i.e. pre-MMX) Pentium cores that have been enhanced with very wide vector floating-point resources and ganged together to make the brains of a flexible, x86-based GPU.

You're probably wondering why Intel picked the old P54C to base Larrabee off of, instead of, say, the later P55 part with MMX. The reason, which Gelsinger did not reveal to heise.dk and which comes from a source of mine, is a bit surprising, in that it involves the Pentagon.
Say "Pentagon Pentium" five times fast

Quite some time ago, after the Pentium was obsolete and Intel had moved on, the company gave the RTL code for the processor to the Pentagon so that the military could continue to fabricate a radiation hardened version of it for use in military applications. Trailing-edge hardware like the Pentium has the advantage of having been thoroughly tested and debugged (cf. the P54C's infamous FDIV bug), and at the time the military had its own fab facilities that could do some low-volume fabrication. (I'm sure they still have such facilities for prototyping.) So the Pentagon cleaned up the P54C's RTL code and began producing a rad-hard version of the chip for military use.

A few years later, when the Pentagon had moved on from the P54C, they offered the RTL back to Intel. So Intel took the core, which has a very small footprint and by this time had been pretty thoroughly debugged, and modified it for use in the many-core chip that later became Larrabee.
Speaking of five times fast

While I'm just spilling all kinds of Larrabee beans, I might as well drop another, performance-related tidbit that came my way. In an upcoming SIGGRAPH paper, Intel will claim that Larrabee has 20x the performance per watt of a Core 2 Duo and half the single-threaded performance. It also has a 4MB coherent L2, and three-operand vector instructions.

Note that I don't have any more context for the information I just gave, so I'm not sure if "halfthe performance of Core 2 Duo" is a clock-for-clock figure or not. If it is, recall that the Pentium's pipeline is less than half the depth of Core 2's, so if the GPU does debut in the 1.7GHz to 2.5GHz range, then that will help it in Core 2 comparisons. The other big unknown is the type of workload that Intel is using for this ballpark performance figure. When it comes to in-order (i.e., Larrabee) vs. out-of-order (i.e., Core 2) and short pipeline vs. long pipeline, the type of workload involved makes all the difference. So these few details that I've given tell you a lot less than you might think at first; but something is better than nothing—and nothing is what we have so far about Larrabee's peformance.
http://arstechnica.com/news.ars/post...ech-sorta.html

Crikey.

Well, if we're not sure it's gonna be fast, we know it'll be 'weird and interesting' at least.

http://www.siggraph.org/s2008/attend...e=papers&id=34
Quote:
Larrabee: A Many-Core x86 Architecture for Visual Computing
This paper introduces the Larrabee a many-core hardware architecture, a new software rendering pipeline, a many-core programming model, and performance analysis for several applications. Larrabee uses multiple in-order x86 CPU cores that are augmented by a wide vector processor unit, as well as fixed-function co-processors. This provides dramatically higher performance per watt and per unit of area than out-of-order CPUs on highly parallel workloads and greatly increases the flexibility and programmability of the architecture as compared to standard GPUs.
AUTHORS

Larry Seiler
Doug Carmean
Eric Sprangle
Tom Forsyth
Intel Corporation

Michael Abrash
RAD Game Tools

Pradeep Dubey
Stephen Junkins
Adam Lake
Intel Corporation

Jeremy Sugerman
Stanford University

Robert Cavin
Roger Espasa
Ed Grochowski
Toni Juan
Intel Corporation

Pat Hanrahan
Stanford University
http://graphics.stanford.edu/~yoel/
http://graphics.stanford.edu/~hanrahan/
Edited by bowman - 7/8/08 at 7:41pm
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post #2 of 6
Why did the compare its power to a cpu?

We want graphics performance numbers people :/
post #3 of 6
When he said he doesn't tell us much, he really meant it.
I'm just pulling numbers out of my ass here, but it's likely that most high end GPUs have more than 20x performance per watt than a C2D... but like he said, it depends on the workload.

So he told us nothing new. Great.
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post #4 of 6
Quote:
Originally Posted by TnB= Gir View Post
Why did the compare its power to a cpu?

We want graphics performance numbers people :/
Because Intel doesn't have a GPU that most of the audience could name off hand. This was my biggest worry with Larrabee, that Intel would treat it as just another marketing gimmick, another enterprise part. Or maybe they realized that Julesworld had beaten them to the punch with existing consumer-purchasable ATi hardware, which ATi has already shown off, and I have to think that the 4870X2 will likely have some sort of demo that the home user can run very soon after the hardware release.
post #5 of 6
"secret Pentagon tech"?

Someone wants views.
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post #6 of 6
Quote:
(I'm sure they still have such facilities for prototyping.)
The US military is still operating fabs producing 130nm coppermine (PIII Tualatins, or a modified derivitave) cores for use in their hardware. Laptops they go in are rated for temperature extremes of -60F to +140F ambient, can be dropped 4 stories, then submerged (case closed) in 30 meters of water and retain their functionality. They still get wiped out by EM pulses from nuclear blasts though.......
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