IEEE Says Multicore is Bad News For Supercomputers

Richard Kelleher writes "It seems the current design of multi-core processors is not good for the design of supercomputers. According to IEEE: 'Engineers at Sandia National Laboratories, in New Mexico, have simulated future high-performance computers containing the 8-core, 16-core, and 32-core microprocessors that chip makers say are the future of the industry. The results are distressing. Because of limited memory bandwidth and memory-management schemes that are poorly suited to supercomputers, the performance of these machines would level off or even decline with more cores.'"

Comments

The problem allegedly being..

[Junta]

For a given node count, we've seen increases in performance. The claimed problem is that for the workloads that concern these researchers, they don't see people mentioning significant enhancements to the fundamental memory architecture projected to follow the scale at which multi-core systems go. So you buy a 16 core chip system to upgrade your quad-core based system and hypothetically gain little despite the expense. Power efficencies drop and getting more performance requires more nodes. Additionally, who is to say that clock speeds won't lower if programming models in the mass market change such that distributed workloads are common and single-core performance isn't all that impressive.

All that said, talk beyond 6-core/8-core is mostly grandstanding at this time. As memory architecture for the mass market is not considered as intrinsically exciting, I would wager there will be advancements that no one speaks to. For example, Nehalem leapfrogs AMD memory bandwidth by a large margin (like by a factor of 2). It means if Shanghai parts are considered satisfactory today to get respectable yield memory wise to support four cores, Nehalem, by a particular metric, supports 8 equally satisfactorily. The whole picture is a tad more complicated (i.e. latency, numbers I don't know off hand), but the one metric is a highly important one in the supercomputer field.

For all the worry over memory bandwidth though, it hasn't stopped supercomputer purchasers from buying into Core2 all this time. Despite improvements in their chipset, Intel Core2 still doesn't reach AMD performance. Despite that, people spending money to get into the Top500 still chose to put their money on Core2 in general. Sure, Cray and IBM supercomputers in the Top2 used AMD, but from the time of its release, Core2 has decimated AMD supercomputer market share despite an inferior memory architecture.

Re:Time for vector processing again

[TapeCutter]

"Multi-Core technology is good for desktop systems as it is meant to run a lot of relatively small apps Rarely taking advantage of more then 1 or 2 cores. per app.In other-words it allows Multi-Tasking without a penalty. We don't use super computers that way. We use them to to perform 1 app that takes huge resources that would take hours or years on your PC and spit out results in seconds or days."

Sorry but that's not entirely correct, most super computers work on highly parallel problems using numerical analysis techniques. By definition the problem is broken up into millions of smaller problems that make ideal "small apps", a common consequence is that the bandwidth of the communications between the 'small apps' becomes the limiting factor.

"Back in the early-mid 90's we had different processors for Desktop and Super Computers."

The earth simulator was refered to in some parts as 'computenick', it's speed jump over it's nearest rival and longevity at the top marked the renaissance of "vector processing" after it had been largely ignored during the 90's.

In the end a supercomputer is a purpose built machine, if cores fit the purpose then they will be used.