Assume that a design team is considering enhancing a machine by adding MMX (mult

Question

Assume that a design team is considering enhancing a machine by adding MMX (multimedia extension instruction) hardware to a processor. When a computation is run in MMX mode on the MMX hardware, it is 10 times faster than the normal mode of execution. Call the percentage of time that could be spent using the MMX mode the percentage of media enhancement.

What percentage of media enhancement is needed to achieve an overall speedup of 2?

What percentage of the run-time is spent in MMX mode if a speedup of 2 is achieved?

Explanation / Answer

(a)What percentage of media enhancement is needed to achieve an overall speedup of 2?

Ans-

We will use Amdahl’s Law for this question. Execution time with Media Enhancement = (Execution time improved by Media enhancement)/(Amount of Improvement) + Execution time unaffected Let x be the percent of media enhancement needed for achieving an overall speedup of 2. Then, (100)/2 = (x)/10 + (100-x) Solving for x, we have x = 55.55

(b)What percentage of the run-time is spent in MMX mode if a speedup of 2 is achieved?

Ans-

The new overall time is 100/2 = 50. Now 55.55 of the original program used media enhancement. Let x be the percentage of the new run-time that is spent in MMX mode (for a speedup of 2). x = (55.55 *50)/100 = 27.78

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