Cache Performance

Cache Performance

• There are 3 formula need to memorize:

1. Memory stall cycles

2. CPU time
= (CPU execution cycles + Memory stall cycles) x Cycle time

3. Average memory access time (AMAT)

= Hit time + (Miss rate x Miss penalty)

More Cache Performance Formula

n

nCan split access time into instructions & data:

pAverage. memory. access. time =
(% instruction accesses) × (instruction. memory. access time) + (% data accesses) × (data memory. access time)

nAnother simple formula:

pCPU time = (CPU execution clock cycles + Memory stall clock cycles) × cycle time

nCan break stalls into reads and writes:

pMemory stall cycles =
(Reads × read miss rate × read miss penalty) + (Writes × write miss rate × write miss penalty)

Performance Summary

1. Improving Cache Performance

2. The organization of a memory system affects its  performance.

--The cache size, block size, and associativity affect the miss rate.

--We can organize the main memory to help reduce miss penalties. For example, interleaved memory supports pipelined data accesses.

3.Can’t neglect cache behavior when evaluating system performance