What is the best way to measure cache performance?

2 Average memory access time

Another important metric for cache performance is the average memory access time (AMAT). This is the average time it takes to access data or instructions from the memory hierarchy, which includes the cache and the main memory. The AMAT depends on the cache hit time, the cache miss rate, and the miss penalty. The cache hit time is the time it takes to access data or instruction from the cache, which is usually much smaller than the main memory access time. The miss penalty is the additional time it takes to access data or instruction from the main memory when a cache miss occurs, which may include the time to transfer the data or instruction from the main memory to the cache. The AMAT can be calculated as: AMAT = cache hit time + (cache miss rate x miss penalty) The lower the AMAT, the better the cache performance, as it means that the memory hierarchy can deliver data or instructions faster to the processor.

3 Cache efficiency and effectiveness

Another way to measure cache performance is to use cache efficiency and effectiveness metrics. Cache efficiency measures how well the cache utilizes its available space, while cache effectiveness measures how well the cache reduces the main memory traffic. Cache efficiency can be expressed as the ratio of the number of useful cache blocks to the total number of cache blocks, where a useful cache block is one that has been accessed at least once since it was loaded into the cache. Cache effectiveness can be expressed as the ratio of the number of main memory accesses without the cache to the number of main memory accesses with the cache, which reflects how much the cache reduces the main memory bandwidth demand. Both cache efficiency and effectiveness can range from 0 to 1, where 1 means perfect performance.

4 Performance counters and simulation tools

How can you obtain the values of these metrics for a given cache design and configuration? One option is to use performance counters, which are hardware registers that can count various events related to the cache, such as cache hits, cache misses, cache accesses, and main memory accesses. Performance counters can be accessed by software tools that can monitor and analyze the cache behavior and performance. Another option is to use simulation tools, which are software programs that can model and emulate the cache and the memory hierarchy, and generate statistics and reports on the cache performance. Simulation tools can be useful for testing and comparing different cache designs and configurations, as well as different workloads and scenarios.

5 Workload and scenario selection

Finally, it is important to note that cache performance is not only dependent on the cache design and configuration, but also on the workload and scenario that the cache is serving. Different workloads and scenarios may have different characteristics, such as data size, access pattern, locality, and temporal and spatial behavior, that affect the cache performance. Therefore, it is essential to select appropriate workloads and scenarios that represent the intended or realistic use cases of the cache, and measure the cache performance under various conditions and parameters. This can help to obtain more accurate and meaningful results, and to identify the strengths and weaknesses of the cache performance.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?