Title: Performance Example Problems from Slides
Class: CSCI 370.50A
Name:  ...

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1) Suppose processor A takes 10 s, and B 15 s. How much faster is A than
B?

s = P_a / P_b = T_b / T_a = 15 s / 10 s = ## 1.5 ##

A is 1.5 times faster, or equivalently, (1.5 - 1) * 100% = 50% faster. 

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2) Suppose a processor has a clock speed of 2.5 GHz. What is the cycle
time?

tau = 1 / f = 1 / (2.5e9 c/s) = 0.4e-9 s / c = ## 0.4 ns / c ##

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3) CPU A has a 2 GHz clock and takes 10 s to perform a task. We are
designing CPU B, and would like it to take 6 s for the same task. We
can use a faster clock in B, but doing so causes it to use 20% more
clock cycles than A. How fast must CPU B's clock be?



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4) CPU A has a cycle time of 250 ps, and a CPI of 2.0. CPU B has a
cycle time of 500 ps, and a CPI of 1.2. Both CPUs run the same
program, and implement the same ISA. Which is faster and by how much?



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5) Show below are data for alternative compiled code sequences using
instructions in three classes (A, B, and C). Find the clock cycles and
average CPI for both sequences.

Class	        A     B     C
=============================
CPI	    	1     2     3
IC in Seq 1     2     1     2
IC in Seq 2     4     1     1


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6) Suppose a new CPU has 85% of the capacitive load of the old one,
and reduces voltage and frequency by 15%. What's the overall power
reduction?



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7) Suppose a program takes 100 s to run, and multiplies account for 80
s. How much do we need to improve multiply performance to get an
overall speedup of 5 overall?



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