I’m writing a series of posts based on my
Shmoocon talk. In this post, I’m going to discuss “multi-core scaling”.
In the decade leading to 2001, Intel CPUs went from 33-MHz to 3-GHz, a
thousand-fold hundred-fold increase in speed. In the decade since, they’ve been stuck at 3-GHz. Instead of faster clock speeds, they’ve been getting more logic. Instead of one instruction per clock cycle, they now execute four (“superscalar”). Instead of one computation per instruction, they now do eight (“SIMD”). Instead of a single CPU on a chip, they now put four (“multi-core”).
However, desktop processors have been stuck at four cores for several years now. That’s because the software is lagging. Multi-threaded software goes up to about four cores, but past that point, it fails to get any benefit from additional cores. Worse, adding cores past four often makes software go slower.
