Intelovi Larrabee GPGPU je zasnovan na staroj Pentium arhitekturi

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


In a recent interview with German tech site heise.de, Intel's Pat Gelsinger let slip* there's 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.
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Update: Intel contacted me to clarify that Gelsinger did not, in fact, tell heise.de that Larrabee was based on P54C. This was something that was apparently mangled in the Babelfish translation, and Andreas at heise.de was pulling the P54C detail from some other source. Nonetheless, I had already heard the information about the Larrabee-Pentium-Pentagon connection from a source of my own, so I do vouch for it.

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.de 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

Pentium still lives.

[Mickie]

Pentagon ???

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