Memory Hierarchy

If the L1 miss rate (as a fraction of all accesses) is 4% and the L2 global miss rate (the fraction of all accesses that also miss in L2) is 1%, what is the L2 local miss rate?

  1. A25%
  2. B4%
  3. C1%
Show answer and explanation

Answer: A. 25%

The local miss rate is the fraction of accesses reaching a cache that miss there. L2 receives the 4% of all accesses that miss in L1, and 1% of all accesses miss in L2 as well, so the local miss rate is 1 ÷ 4 = 25%. The high local rate does not mean L2 is ineffective; L2 only sees the low-locality accesses L1 could not capture. 1% is the global miss rate relative to all accesses, and 4% is the L1 miss rate.

  • A. Correct. 1% out of the 4% reaching L2 gives 25%.
  • B. 4% is the L1 miss rate.
  • C. 1% is the global miss rate relative to all accesses.
Practice this topic Back to topic

More Memory Hierarchy questions

  1. With 64 TLB entries and a 4 KB page size, how much memory can be accessed without TLB misses (the TLB reach)?
  2. Which pair correctly states the main advantage and drawback of using large pages (huge pages)?
  3. When each row of a 2D array is 4,096 bytes (a power of two), walking down a column can cause many misses even though the cache has spare capacity. Which countermeasure is effective?
  4. Roughly how many times longer is a main-memory DRAM access than an L1 cache hit (for typical PC or server CPUs)?
  5. What is the role of the valid bit attached to each cache line?