GATE CS 2024 Set 1 — Question 56
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Computer Organization & Architecture → Memory Hierarchy & Cache → Cache Numericals
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Question
A given program has 25% load/store instructions. Suppose the ideal CPI (cycles per instruction) without any memory stalls is 2. The program exhibits 2% miss rate on instruction cache and 8% miss rate on data cache. The miss penalty is 100 cycles. The speedup (rounded off to two decimal places) achieved with a perfect cache (i.e., with NO data or instruction cache misses) is _________
Correct answer
3 to 3
Solution
To calculate the speedup achieved with a perfect cache, we compare the execution time (or CPI) of the program with the actual cache to the execution time with a perfect cache.1. Identify Given Parameters:
A perfect cache has a 0% miss rate, meaning there are no memory stalls.5. Calculate Speedup:The speedup achieved with a perfect cache is 3.00.
- Ideal CPI () = 2
- Percentage of load/store instructions = 25% = 0.25
- Instruction cache miss rate () = 2% = 0.02
- Data cache miss rate () = 8% = 0.08
- Miss penalty () = 100 cycles
- Instruction Fetch Stalls: Every instruction requires a fetch from the instruction cache.
- Data Access Stalls: Only load/store instructions access the data cache.
- Total Stalls per Instruction:
A perfect cache has a 0% miss rate, meaning there are no memory stalls.5. Calculate Speedup:The speedup achieved with a perfect cache is 3.00.
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