Some of Nvidia's CPU architects gave a talk at the Hot Chips symposium today, and they revealed some long-awaited details about Nvidia's first custom CPU design. We weren't able to attend the talk, but the firm evidently pre-briefed some analysts about what it planned to say. There's a free-to-download whitepaper at Tirias Research on the Denver CPU core, and I've been scanning it eagerly to see what we can learn.
We already know Denver is a beefier CPU than ARM's Cortex-A15, since two Denver cores replace four A15 cores in the Denver-based variant of the Tegra K1. We also know Denver is, following Apple's Cyclone, the second custom ARM core to support the 64-bit ARMv8 instruction set architecture. We've long suspected other details, but Nvidia hasn't officially confirmed much—until now.
Here are some highlights of the Denver information revealed in the whitepaper and presumably also in the Hot Chips presentation:
Execution is wide but in-order. Denver attempts to save power and reap the benefits of dynamic code optimization by eschewing power-hungry out-of-order execution hardware in favor of a simpler in-order engine. That execution engine is very wide: seven-way superscalar and thus capable of processing as many as seven operations per clock cycle. Denver's peak instruction throughput should be very high. The tougher question is what its typical throughput will be in end-user workloads, which can be variable enough and contain enough dependencies to challenge dynamic optimization routines. In other words, Denver's high peak throughput could be accompanied by some fragility when it encounters difficult instruction sequences.
We should know more soon. Nvidia says Tegra K1 64 devices should be available "later this year" and alludes to its new SoC as an Android L development platform. I can't wait to put one of these things through its paces.
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