An ISA has the following instruction group: a) If a CPU that runs at 1 GHz imple
ID: 3685003 • Letter: A
Question
An ISA has the following instruction group:
a) If a CPU that runs at 1 GHz implements this ISA, what is the average rate of instructions execution, IPS (Instructions Per Second)?
b) If a benchmark program has an execution time of 1 second when it runs on the CPU of part (b), what is the IC of that program?
c) If you have the chance to improve the CPI of, just, one of the 4 instruction groups, which group would you improve? Why?
Group Frequency CPI load/store 30% 3 Arithmetic & Logic 40% 1 Multiplication and Division 10% 8 Jump and Branch 20% 2Explanation / Answer
CPU runs at 1Ghz
Average rate of instruction:
A 1hz clock has a (1 / (1 * 10^9) )*10^12 = 100npicoseconds(ps) cycle time
Group Frequency CPI CPI x F
load/store 30% 3 9
Arithmetic & Logic 40% 1 0.4
Multiplication and Division 10% 8 0.8
Jump and Branch 20% 2 0.2
---------------------------------------------------------------------
2.3
Cycles per instructions: i=1 to n sigma (CPI x F)
Total= 9+0.4+0.8+0.2 =2.3
So, to improve performance (everything else being equal) increasethe # of required cycles for a program,
the clock cycle time or, said another way,
the clock rate. is
Seconds / Program = cycles/ program * seconds/ cycle