In each of the following three cases, calculate the CPI for a processor with the
ID: 3695751 • Letter: I
Question
In each of the following three cases, calculate the CPI for a processor with these specifications:
Base CPI=2
Processor speed=2 GHz
Main memory access time=100ns
First-level cache miss rate per instruction=7%
(a) We only have a first level (L1) cache
(b) Along with L1 cache, we also have a second level direct-mapped cache in which . Second-level cache direct-mapped speed=12 cycle . Global miss rate with second-level cache direct-mapped=3.5%
(c) Along with L1 cache, we also have a second level 8-way set associative cache in which: .Second-level cache 8-way set-associative speed=28 cycle .Global miss rate with second-level cache 8-way set-associative=1.5%
Explanation / Answer
1. Base CPI=2
2. Processor speed=2 GHz
3. Main memory access time=100ns
4. First-level cache miss rate per instruction=7%
(a) We only have a first level (L1) cache
First-level cache CPI = Base CPI + Memory-Stall Cycles per Instruction
Memory-Stall Cycles per Instruction = Miss Penalty (in cycles) x Miss Rate
Miss penalty = Main Memory Access Time / (1/Processor Speed)
=100ns / (1/2 GHz)= 200 cycles
First-level Cache CPI = 2 + (0.07 * 200) = 16
(b) Along with L1 cache, we also have a second level direct-mapped cache in which second-level cache direct-mapped speed=12 cycle. Global miss rate with second-level cache direct-mapped=3.5%
L2 hit time = 12cycles
L2 global miss rate = 3.5%
Total CPI= Base CPI+(L1 miss rate *L2 hit time)+(L2 global miss rate *L2 miss time)
Total CPI=2+(0.07*12)+(0.035*200)=9.84
L2 8-way set cache hit time=28cycles
L2 8-way set cache global miss rate = 1.5%
Total CPI=Base CPI+ ( L1 miss rate * L2 hit time ) + (L2 global miss rate * L2 miss time )
Total CPI= 2+ (0.07*28 ) + ( 0.015*200 )=6.96
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