Reverse Multithreading CPUs

microbee writes "The register is reporting that AMD is researching a new CPU technology called 'reverse multithreading', which essentially does the opposite of hyperthreading in that it presents multiple cores to the OS as a single-core processor." From the article: "The technology is aimed at the next architecture after K8, according to a purported company mole cited by French-language site x86 Secret. It's well known that two CPUs - whether two separate processors or two cores on the same die - don't generate, clock for clock, double the performance of a single CPU. However, by making the CPU once again appear as a single logical processor, AMD is claimed to believe it may be able to double the single-chip performance with a two-core chip or provide quadruple the performance with a quad-core processor."

Comments

No, superscalar is different

[overshoot]

Superscalar refers to having multiple execution paths inside of a single processor, allowing the dispatch of multiple instructions in a single clock cycle. However, the register sets (etc.) maintain a common state (although keeping the out-of-order updates straight sucks a huge amount of complexity and power.)

In this case, AMD appears to be trying to decouple the states enough that the out-of-order resolution doesn't require micromanaging all of the processes from a single control point.

Or maybe predicting both branches?

[silverdirk]

As one reply stated, you can't know which is right unless you had 3 cores.

But, with two cores, you could have a way to predict "branch" and "not branch" at every prediction spot. The core that gets it right sends the registers to the other core so they can continue as if every branch were predicted correctly...

That would only work if you had a nice fast way to copy registers accross in a very small number of clock cycles... so again, just a bunch of speculation. But it was a neat enough idea I had to say it.