An old program is parallelized so that it runs faster on

modern multicore processors.

a. The speedup of the parallelize version over the single-threaded version

is significantly less than the number of processors. What could be one

cause?

b. You modify the program to fix this first performance issue. However,

now you find that the program is slowed down by a global state update

that must happen in only a single thread after every parallel

computation. In particular, your program performs 90% of its work

(measured as processor-seconds) in the parallel portion and 10% of its

work in this serial portion. The parallel portion is perfectly

parallelizable. What is the maximum speedup of the program if the

multicore processor had an infinite number of cores?

c. How many processors would be required to attain a speedup of 4?