Re:Ask HN: Why are modern Intel CPUs not getting a lot more ...
by amelius on Wednesday August 17, 2016 @08:44AM
(#12304195)
Also could it be that bigger caches would require more coherence-logic (or even a more complicated/congested cache-bus), making everything slower, and eventually negating the advantage of more cores?
Re:Ask HN: Why are modern Intel CPUs not getting a lot more ...
by imtringued on Wednesday August 17, 2016 @09:59AM
(#12304707)
You can make cache coherence scale to multiple cores with precise tracking and the overhead of precise tracking can be reduced by arranging your cores as clusters.
Exact tracking basically requires a bit field with one bit for each core. The problem is with the storage overhead since a 64 core cpu would need 64 bits per cache line. However if you had a 64 core CPU you could partition it into 8 clusters with 8 cores each which means you only need 8 bits per cache line for exact tracking.
http://www.cis.upenn.edu/acg/papers/cacm12_why_coherence.pdf
Bigger caches that would be required by more cores in order to keep the "usefulness" of the design in balance, would lead to higher power consumption, which a) is a primary criterium of evaluation of the product such as laptops, even before the computing power; b) not justified given typical "office+home" workload, as already mentioned in the answers.