Profile with Valgrind Callgrind and View in KCachegrind

Deterministic Profiling Without Hardware Counters

Valgrind's Callgrind simulates every instruction, so results are repeatable across machines even when hardware perf events are blocked in containers. KCachegrind turns Callgrind output into inclusive and exclusive cost views. It is slower than perf by 10x/50x, but invaluable when you need exact call counts on a laptop without perf permissions.

Reading Inclusive vs Exclusive Cost

Inclusive cost counts time in a function plus everything it called. Exclusive cost is time spent inside the function body only. A high inclusive, low exclusive node means the callee is the real problem.

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• Run the smallest input that still exercises the slow path
• JIT and self-modifying code confuse simulators; test native C first
• Compare two callgrind.out files with callgrind_annotate --diff
• Massif pairs well when allocations correlate with hot paths

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 profile a C program with Callgrind and interpret the annotated output. This exercise asks you to name the top three inclusive-cost functions and explain what each one does in your call graph.