How are cache memories shared in multicore Intel CPUs?

Question

I have a few questions regarding Cache memories used in Multicore CPUs or Multiprocessor systems. (Although not directly related to programming, it has many repercussions wh

Answer 1

To answer your first, I know the Core 2 Duo has a 2-tier caching system, in which each processor has its own first-level cache, and they share a second-level cache. This helps with both data synchronization and utilization of memory.

To answer your second question, I believe your assumption to be correct. If the processors were to be able to access each others' cache, there would obviously be less cache misses as there would be more data for the processors to choose from. Consider, however, shared cache. In the case of the Core 2 Duo, having shared cache allows programmers to place commonly used variables safely in this environment so that the processors will not have to access their individual first-level caches.

To answer your third question, there could potentially be a problem with accessing other processors' cache memory, which goes to the "Single Write Multiple Read" principle. We can't allow more than one process to write to the same location in memory at the same time.

For more info on the core 2 duo, read this neat article.

http://software.intel.com/en-us/articles/software-techniques-for-shared-cache-multi-core-systems/