SMP/dual (multi) core phase II

[me at mattgillen.net (Matthew Gillen)]

Dan Ritter wrote:
> On Sun, May 06, 2007 at 09:47:08PM -0400, markw at mohawksoft.com wrote:
>> Please explain what you mean. "Hyperhreading" CPUs are multi-core CPUs,
>> aren't they, or am I missing something?
> 
> Nope. HyperThreading CPUs are complex single CPUs with the
> ability to run in two modes: one is a full capacity single core,
> and the other is two lower-capacity cores which share
> significant on-chip resources.

The most significant of which is the cache.  The reason Hyperthreading is
slower than single processors for some workloads is that you can get into this
cache-thrashing situation that mucks up the pipelining really badly.

They learned their lesson, and now all multi-core CPUs have independent caches.

There's still sort of a bottleneck to main memory, but you can't get over that
unless you go NUMA.

Matt

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