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What a peculiar design. They went for an in order design instead of the out-of-order design that has been standard in high-end ARM cores for years. Out-of-order
by DCKing 12y ago
What a peculiar design. They went for an in order design instead of the out-of-order design that has been standard in high-end ARM cores for years. Out-of-order usually brings more instructions per clock cycle ("more efficient"), but makes the chip more power hungry and makes it harder to achieve a high clock speed.
So the in-order design they have now allows them to scale up to 2.5 GHz which is very high for such a constrained chip. They also have this weird "code optimizer" that appears to sacrifice some RAM and a CPU core to dynamically reorganize processor instructions to run better on this in-order design. It seems as though they want to have their cake and eat it too, but at the same time they appear to paradoxically introduce complexity to achieve simplicity.
I wonder if someone more knowledgable about chip design could comment on this design?
- _delirium 12y agoOne of the more interesting bits of speculation about the design's motivations that I've seen so far is an anonymous comment on the Slashdot version of this story: http://hardware.slashdot.org/comments.pl?sid=5519563&cid=47653679 http://hardware.slashdot.org/comments.pl?sid=5519563&cid=476...
- gcp 12y agoThis is another good post, despite the appeal to authority: http://hardware.slashdot.org/comments.pl?sid=5519563&cid=47654085 http://hardware.slashdot.org/comments.pl?sid=5519563&cid=476... Saying "When an in-order CPU stalls on memory, it's still burning power while waiting, while an OOO processor is still getting work done" seems deceptive, though. The OOO processor is (often) doing speculative work, which may be unneeded, and a stalled in-order CPU won't be using quite the same amount of power as if the execution units were actually switching. Though I'm pretty sure the NVIDIA design must speculative prefetch and hoist memory reads aggressively to be performance competitive (see the huge cache sizes!), which also burns power.
- wmf 12y agoIt's Transmeta 2.0.