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Can anyone explain what the practical differences between something like this and a gpgpu approach? It doesn't sound particularly performant compared to modern

by trotsky 13y ago

Can anyone explain what the practical differences between something like this and a gpgpu approach? It doesn't sound particularly performant compared to modern gpus otherwise. Maybe they add in some more general purpose instructions for a little more flexibility?

dagurp 13y ago
If nothing else it's very small and uses very little power
vidarh 13y ago
A typical GPU can execute a small number of threads on a large number of streams of data carefully laid out in memory. Every time you want to do something conditionally on just one data stream, you waste a lot of capacity. In contrast, the Epiphany chips can execute individual threads on each core in parallel on data either local to the core (fastest), on any other core, or in separate main memory. The current Epiphany chips aren't too spectacular, since the core count is "low". They can "only" execute 16 individual instruction streams in parallel. But that's on a chip the size of your finger nail, and their roadmap is aiming for 1024 core chips. They're effectively aiming for people to find ways of making effective use of simple, small, power efficient cores for problems that are not "data parallel" enough to be efficiently done on GPU's.
- UnoriginalGuy 13y ago
  This might be a really stupid question: How difficult would it be in the practical sense to keep all of the cores on something like this "fed" with enough information to get benefits from its concurrency? I mean to "feed" all 64 cores enough data/code so they can all "do something" concurrently is one hell of a job all on its own!
  - vidarh 13y ago
    Depends a lot on the type of problem, and I think that's going to be what makes or breaks them. They have some good examples, but you're right, it's a hard problem and one of the reasons it's so important for them to get these dev boards out.
- trotsky 13y ago
  Awesome explanation, thanks. I love that you can learn about things outside your field here without it being super dumbed down or having to google half a dozen domain specific terms.

by trotsky 13y ago

dagurp 13y ago

If nothing else it's very small and uses very little power

vidarh 13y ago

A typical GPU can execute a small number of threads on a large number of streams of data carefully laid out in memory. Every time you want to do something conditionally on just one data stream, you waste a lot of capacity. In contrast, the Epiphany chips can execute individual threads on each core in parallel on data either local to the core (fastest), on any other core, or in separate main memory. The current Epiphany chips aren't too spectacular, since the core count is "low". They can "only" execute 16 individual instruction streams in parallel. But that's on a chip the size of your finger nail, and their roadmap is aiming for 1024 core chips. They're effectively aiming for people to find ways of making effective use of simple, small, power efficient cores for problems that are not "data parallel" enough to be efficiently done on GPU's.

UnoriginalGuy 13y ago
This might be a really stupid question: How difficult would it be in the practical sense to keep all of the cores on something like this "fed" with enough information to get benefits from its concurrency? I mean to "feed" all 64 cores enough data/code so they can all "do something" concurrently is one hell of a job all on its own!
- vidarh 13y ago
  Depends a lot on the type of problem, and I think that's going to be what makes or breaks them. They have some good examples, but you're right, it's a hard problem and one of the reasons it's so important for them to get these dev boards out.
trotsky 13y ago
Awesome explanation, thanks. I love that you can learn about things outside your field here without it being super dumbed down or having to google half a dozen domain specific terms.