Fundamentals of Quantitative Design and Analysis - Computer Architecture: A Quantitative Approach - page 68

c. [20] <1.2> Figure 1.3 shows, on average, the cost of downtimes, assuming that the cost
is equal at all times of the year. For retailers, however, the Christmas season is the most
proitable (and therefore the most costly time to lose sales). If a catalog sales center has
twice as much traffic in the fourth quarter as every other quarter, what is the average
cost of downtime per hour during the fourth quarter and the rest of the year?
1.13 [10/20/20] <1.9> Your company is trying to choose between purchasing the Opteron or
Itanium 2. You have analyzed your company's applications, and 60% of the time it will be
running applications similar to wupwise, 20% of the time applications similar to ammp,
and 20% of the time applications similar to apsi.
a. [10] If you were choosing just based on overall SPEC performance, which would you
choose and why?
b. [20] What is the weighted average of execution time ratios for this mix of applications
for the Opteron and Itanium 2?
c. [20] What is the speedup of the Opteron over the Itanium 2?
1.14 [20/10/10/10/15] <1.9> In this exercise, assume that we are considering enhancing a ma-
chine by adding vector hardware to it. When a computation is run in vector mode on the
vector hardware, it is 10 times faster than the normal mode of execution. We call the per-
centage of time that could be spent using vector mode the percentage of vectorization . Vectors
are discussed in Chapter 4 , but you don't need to know anything about how they work to
answer this question!
a. [20] <1.9> Draw a graph that plots the speedup as a percentage of the computation per-
formed in vector mode. Label the y -axis “Net speedup” and label the x -axis “Percent
vectorization.”
b. [10] <1.9> What percentage of vectorization is needed to achieve a speedup of 2?
c. [10] <1.9> What percentage of the computation run time is spent in vector mode if a
speedup of 2 is achieved?
d. [10] <1.9> What percentage of vectorization is needed to achieve one-half the maxim-
um speedup atainable from using vector mode?
e. [15] <1.9> Suppose you have measured the percentage of vectorization of the program
to be 70%. The hardware design group estimates it can speed up the vector hardware
even more with significant additional investment. You wonder whether the compiler
crew could increase the percentage of vectorization, instead. What percentage of vec-
torization would the compiler team need to achieve in order to equal an addition 2×
speedup in the vector unit (beyond the initial 10×)?
1.15 [15/10] <1.9> Assume that we make an enhancement to a computer that improves some
mode of execution by a factor of 10. Enhanced mode is used 50% of the time, measured as a
percentage of the execution time when the enhanced mode is in use . Recall that Amdahl's law
depends on the fraction of the original, unenhanced execution time that could make use of
enhanced mode. Thus, we cannot directly use this 50% measurement to compute speedup
with Amdahl's law.
a. [15] <1.9> What is the speedup we have obtained from fast mode?
b. [10] <1.9> What percentage of the original execution time has been converted to fast
mode?
1.16 [20/20/15] <1.9> When making changes to optimize part of a processor, it is often the
case that speeding up one type of instruction comes at the cost of slowing down something