retagged by
617 views
2 votes
2 votes

The designers of a computer must select a cache system. They have two options.

In first design they uses a direct-mapped cache containing $2$ words per cache line. It would have an instruction miss rate of $3%$ and a data miss rate of $8%$.

In second design they uses a $2$-way set associative cache containing $8$ words per cache line. It would have an instruction miss rate of $1%$ and a data miss rate of $4%$.

For each design, there will be approximately $0.5$ data references on average per instruction. The cache miss penalty in clock cycles is $8$ + cache line size in words; for example, the penalty with $1$-word cache lines would be $8 + 1 = 9$ clock cycles.

Let $D1 =$ cycles wasted by First Design on cache miss penalties (per instruction)

Let $D2 =$ cycles wasted by Second Design  on cache miss penalties (per instruction)

On average, how many clock cycles will be wasted by each on cache miss penalties?

  1. $D1 = 1.10, D2 = 0.96$
  2. $D1 = 0.70, D2 = 0.40$
  3. $D1 = 1.10, D2 = 0.40$
  4. $D1 = 0.70, D2 = 0.48$
retagged by

2 Answers

Best answer
5 votes
5 votes
No of instruction per instruction is 1 and no of data per instruction is 0.5

Direct-mapped cache containing 2 words per cache line. It would have an instruction miss rate of 3% and a data miss rate of 8%.
Miss penality = 0.03(8+2) + 0.08(8+2)/2 = 0.30 + 0.40 = 0.70

2-way set associative cache containing 8 words per cache line. It would have an instruction miss rate of 1% and a data miss rate of 4%.
Miss penality = 0.01(8+8) + 0.04(8+8)/2 = 0.16 + 0.32 = 0.48
selected by
0 votes
0 votes

For these designs,

let p equal the cache miss penalty, in clock cycles, and let mi and md indicate the instruction and data miss rates, respectively.

Then the total time spent on penalties, for an average instruction, is p * (1 * mi + 0.5 md), since there are about 0.5 data references per instruction.

Consequently, the total penalty for D1 and D2, are 0.70 and 0.48, respectively.

Answer:

Related questions

3 votes
3 votes
2 answers
4