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GATE CSE 2024 Session 1 Q55: Core count minimising time with per-core overhead

Question

The baseline execution time of a program on a 2 GHz single core machine is 100 nanoseconds (ns). The code corresponding to 90% of the execution time can be fully parallelized. The overhead for using an additional core is 10 ns when running on a multicore system. Assume that all cores in the multicore system run their share of the parallelized code for an equal amount of time.

The number of cores that minimize the execution time of the program is ________

Try it: numerical answer: type the value

Numerical answer. No negative marking.
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Answer: 3 (official GATE 2024 final answer key)

Concept used: Amdahl's law with a linear overhead term.

First step: With nn cores, time =10+90/n+10(n−1)= 10 + 90/n + 10(n - 1) ns; evaluate for small nn.

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Source: official GATE 2024 Session 1 CS question paper and final answer key, organised by IISc Bangalore. Question paper · Answer key

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