Report: Roadblock Ahead for Multi-Core Processors

In case you haven't noticed, multi-core processing has taken hold and the race is on to cram more cores onto a single die. But assuming developers can keep up, at some point, chip manufacturers are going to have address a potential major problem that could make adding more cores a useless endeavor. More specifically, a "memory wall" looms large in the not too distant future that, as Jon Stokes from ArsTechnica puts it, could make more than 16 cores pointless.

The problem stems from memory bandwidth not being able to keep pace with faster processors, whether those speed bumps come from a faster frequency or more cores. Put simply, memory is creating a bottleneck and can't feed the processor fast enough, a problem that has existed for some time. Intel and AMD have been able to mask the problem by adding more cache, but doing so doesn't overcome the memory wall, which looks poised to really rear its ugly head as more cores are piled on to new chip packages.

"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," writes Samuel K. Moore at IEEE Spectrum Online. "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."

According to the simulation, performance gains level out at 8-cores, with 16-core chips performing no better than a dual-core processor. As the core count increases, the performance starts to decline sharply.

One solution Sandia has proposed is to stack memory chips on top of the processor, something both Intel and IBM have been working on. Some might also remember reading about multi-core memory, a new memory architecture developed by cryptographer Joseph Ashwood. But no matter what the eventual solution, someone's going to have to come with something relatively fast. Sixteen core chips might not be as far off as you think, and the memory wall isn't going to crumble on its own.

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