# 2018q3 第 13 週測驗題 ### 測驗 `1` Consider the following C code: ```C long array[1024 * 1024]; for (int x = 0; x < 10; ++x) { for (int i = 0; i < 1024 * 1024; i += 1024) { array[i] += 1; } } ``` Assume that all variables but array are placed into registers and that array is placed in memory such that the address of array is a multiple of the cache block size (i.e. all of its block offset bits are 0). Also, assume that longs are 8 bytes and all caches are initially empty. How many data cache misses will this C code experience on a 64KB (64 * 1024 byte) direct-mapped cache with 64B cache blocks? ==作答區== * `(a)` 1024 + (1024 - 512) * 10 * `(b)` (1024 + (1024 - 512) * 9) * `(c)` ((1024-64) * 10) * `(d)` (1024 + (1024 - 64) * 9) * `(e)` 1024 * `(f)` 10240 --- 測驗 `2` 承測驗 `1` How many data cache misses will this C code experience on a 1.5MB (1536 * 1024 byte) 3-way set associative cache with 64B cache blocks with an LRU replacement policy? ==作答區== * `(a)` 1024 + (1024 - 512) * 10 * `(b)` (1024 + (1024 - 512) * 9) * `(c)` ((1024-64) * 10) * `(d)` (1024 + (1024 - 64) * 9) * `(e)` 1024 * `(f)` 10240 --- 測驗 `3` Consider the following codes: - [ ] Version 0 ```C for (int k = 0; k < N; ++k) { for (int i = 0; i < N; ++i) { for (int j = 0; j < N; ++j) { B[i*N+j] += A[i*N+k] * A[k*N+j]; } } } ``` - [ ] Version 1 ```C for (int kk = 0; kk < N; kk+=2) { for (int i = 0; i < N; ++i) { for (int j = 0; j < N; ++j) { for (int k = kk; k < kk + 2; ++k) { B[i*N+j] += A[i*N+k] * A[k*N+j]; } } } } ``` Assuming n is very large and the compiler does not reorder or omit memory accesses to the arrays, which of the following statements are true: Select one statement that would apply ==作答區== * `(a)` `A[k * N + j]` has better spatial locality in version 1 * `(b)` `A[i * N + k]` has better spatial locality in version 1 * `(c)` `B[i * N + j]` has better spatial locality in version 1 ---