Exercise 5.6 Media applications that play audio or video fi les are part of a class of workloads called “streaming” workloads; i.e., they bring in large amounts of data but do not reuse much of it. Consider a video streaming workload that accesses a 512 KB working set sequentially with the following address stream:

0, 4, 8, 12, 16, 20, 24, 28, 32, …

5.6.1 [5] <5.5, 5.3> Assume a 64 KB direct-mapped cache with a 32-byte line.

What is the miss rate for the address stream above. How is this miss rate sensitive to the size of the cache or the working set? How would you categorize the misses this workload is experiencing, based on the 3C model.

5.6.2 [5] <5.5, 5.1> Recompute the miss rate when the cache line size is 16 bytes, 64 bytes, and 128 bytes? What kind of locality is this workload exploiting?

5.6.3 [10] <5.10> “Prefetching” is a technique that leverages predictable address patterns to speculatively bring in additional cache lines when a particular cache line is accessed. One example of prefetching is a stream buffer that prefetches sequentially adjacent cache lines into a separate buffer when a particular cache line is brought in. If the data is found in the prefetch buffer, it is considered as a hit and moved into the cache and the next cache line is prefetched. Assume a two-entry stream buffer and assume that the cache latency is such that a cache line can be loaded before the computation on the previous cache line is completed. What is the miss rate for the address stream above?

Cache block size (B) can affect both miss rate and miss latency. Assuming the following miss rate table, assuming a 1-CPI machine with an average of 1.35 references (both instruction and data) per instruction, help fi nd the optimal block size given the following miss rates for various block sizes.

8 16 32 64 128

a. 8% 3% 1.8% 1.5% 2%

b. 4% 4% 3% 1.5% 2%

5.6.4 [10] <5.2> What’s the optimal block size for a miss latency of 20 × B cycles?

5.6.5 [10] <5.2> What’s the optimal block size for a miss latency of 24 + B cycles?

5.6.6 [10] <5.2> For constant miss latency, what’s the optimal block size?