Benchmark Programs Using time, perf stat, and hyperfine

Measure Before You Optimize

Brendan Gregg's production performance work at Netflix and Sun starts with simple wall-clock timing, then perf stat, then deeper tools. Guessing where time goes wastes weeks. A three-line time run, a perf stat pass for cycles and cache misses, and hyperfine for repeated comparisons form the baseline toolkit every systems engineer keeps on hand.

What Each Tool Answers

time reports elapsed, user, and system seconds for one run. perf stat samples hardware counters without modifying your binary. hyperfine warms up, runs many iterations, and prints mean plus standard deviation so you can see noise.

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• Wall clock alone cannot separate CPU work from I/O wait
• Counter events explain why a loop is slow, not just that it is
• Always run release builds with the same CPU governor when comparing
• Save baseline numbers before changing code

Working Through the Exercise

Keep the relevant documentation open while you implement. When your output disagrees with the reference, trace one failing case by hand before changing random lines.

• Trace first: walk one failing input step by step
• Read the manual: skim the official doc for the mechanism named in this task
• Compare baselines: save measurements from the prior step so speedups are honest

Why for this exercise

You will benchmark a small C program with time, perf stat, and hyperfine, then print a short comparison table. This exercise asks you to treat measurement as the first optimization step, not an afterthought.