Cache

• load and store is how a CPU gets and puts things into memory
  • analogous to read and write
• loads are very importance when it comes to analyzing the performance of the CPU
• main memory is very slow compared to the CPU circuitry
• to offset this, the CPU uses a layered cache
• L1 Cache
  • Very fast & efficient (3-4 cycles to load)
  • Very small (~32kB)
• L2 Cache
  • Pretty fast (~10-12 cycles to load)
  • Medium (~256kB)
• L3 Cache
  • Fast (~30-70 cycles to load)
  • Large (~8MB)
• Main Memory
  • Slow (~100-150 cycles to load)
  • Very Large (~16GB)
• modern CPUs are multi-core
• each core will have it’s own L1, L2

• the L3 is shared across cores

• the performance penalty from not considering the cache can undo all other performance improvements