計算機組織問題 - 考試

各位大大請問資工系-計算機組織問題



1.The following instruction mix with CPIs is given for Machine A running at a
clock rate of 3.6 GHz. Suppose ALUop instructions can only access operands in
registers. We need to use Load/store instructions for accessing operands in
memory. Analysis show that 20% of the ALUop instructions preceded or followed
by Load/store instructions to access operands from or to memory.

Instruction mix CPI
ALUop 55% 2
Load/store 20% 4
Branch 20% 3
Jump 5% 2

Now Machine A’s hardware is modified, and some ALUmem instructions are added
so that operands can be accessed directly from or to memory. This
modification, however, increases in clock time period by 4%. We call it one
Machine B. What is the maximum CPI of the new ALUmem instructions in order
for Machine B to outperform Machine A in CPU time?

2.Suppose that we can improve the floating point instruction performance of
machine by a factor of 9 (the same floating point instructions run 9 times
faster on this new machine). What percent of the instructions must be
floating point to achieve a Speedup of at least 3?

x= percentage of floating point instructions.
Speedup=3, if the original program executed in 100 cycles, the new program
runs in 100/3 cycles.
(100)/3 = (x)/9 + (100 – x)
Solving for x, we get:
x = 75
The percent of floating point instructions need to be 75.

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