Mixed Signals
Any sufficiently advanced information is indistinguishable from noise
Wednesday 18 April 2007, 6:55 AM
Larrabee leakage...
A quick update on the Larrabee many-core processor that Intel says will get the standard architecture running at teraflops in the next couple of years. The cores (or tiles, which seems to be a new alternative name for the same thing) will talk to each other over a ring network, unlike the 80-core research Polaris chip that's been widely shown off.
Polaris uses a mesh, where cores can pretty much talk to any other core through a hop or two. A ring, last seen in IBM's Token Ring network, passes data in a constantly circulating pattern, each packet visiting each node in sequence before returning to its source. This has the advantage over other architectures in that the timing is exact -- you know precisely how long it will take for information to reach its destination, once you've despatched it -- but doesn't scale well. In the case of processors, a good rule of thumb is that much beyond twenty or so, you'll start to lose more than you gain.
Thus an educated guess would put the number of cores in Larrabee at twenty or fewer. We know from a couple of asides that it has 'tens' of cores, and if we're looking for a teraflops from twenty cores then that's 50 gigaflops/core - which is Moore's Lawable from here, as to the best of my knowledge (and depending on how you define a flops) you can get around 20-25 gigaflops from a current core at full canter.
Another snippet - Larrabee is definitely hetero. Not all those cores will be the same.
Polaris uses a mesh, where cores can pretty much talk to any other core through a hop or two. A ring, last seen in IBM's Token Ring network, passes data in a constantly circulating pattern, each packet visiting each node in sequence before returning to its source. This has the advantage over other architectures in that the timing is exact -- you know precisely how long it will take for information to reach its destination, once you've despatched it -- but doesn't scale well. In the case of processors, a good rule of thumb is that much beyond twenty or so, you'll start to lose more than you gain.
Thus an educated guess would put the number of cores in Larrabee at twenty or fewer. We know from a couple of asides that it has 'tens' of cores, and if we're looking for a teraflops from twenty cores then that's 50 gigaflops/core - which is Moore's Lawable from here, as to the best of my knowledge (and depending on how you define a flops) you can get around 20-25 gigaflops from a current core at full canter.
Another snippet - Larrabee is definitely hetero. Not all those cores will be the same.
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