Media applications that play audio or video files are part of a class of workloa
ID: 3765297 • Letter: M
Question
Media applications that play audio or video files 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, 2, 4, 6, 8, 10, 12, 14, 16, …
a. Assume a 64 KiB direct-mapped cache with a 32-byte block. 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?
b. Re-compute the miss rate when the cache block size is 16 bytes, 64 bytes, and 128 bytes. What kind of locality is this workload exploiting?
c. Prefetching” is a technique that leverages predictable address patterns to speculatively bring in additional cache blocks when a particular cache block is accessed. One example of prefetching is a stream buffer that prefetches sequentially adjacent cache blocks into a separate buffer when a particular cache block 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 block is prefetched. Assume a two-entry stream buffer and assume that the cache latency is such that a cache block can be loaded before the computation on the previous cache block is completed. What is the miss rate for the address stream above?
Explanation / Answer
a)
Compulsory misses.
The miss rate is proportion to the block size. In a 64KB direct-mapped cache, there exists 512K / 32 = 16K misses
b)
In 16byte, 512K/16 = 32K.
In 64byte, 512K/64 = 8K.
In 128byte, 512K/128= 4K.
Spatial locality.