Implement High-Resolution Timer Using clock_gettime

Nanosecond Timing in Userspace

clock_gettime(CLOCK_MONOTONIC) is what glibc, LLVM's benchmark harness, and the Linux kernel's own microbenchmarks use for sub-millisecond timing. Unlike gettimeofday, monotonic clocks never jump backward when NTP adjusts wall time. Pairing start and end reads around a tight loop is the foundation of every custom benchmark harness.

Building a Small Timer API

Read timespec at region start and end, subtract, convert to nanoseconds or microseconds. Warm up caches before the timed region so cold-start effects do not dominate.

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• Never time a single iteration of a nanosecond-scale loop; batch many iterations
• Pin thread to a core when comparing micro-optimizations on laptops
• CLOCK_PROCESS_CPUTIME_ID measures CPU time, not sleep time
• Print both mean and min across several runs

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 implement now_ns() and wrap a benchmark region with warmup plus repeated samples. This exercise asks you to report elapsed time for a known workload and verify results are stable across runs.