Profiling: multiple-choice review
Multiple-choice synthesis across the profiling unit — sampling economics, profile-type selection, flame-graph reading, eBPF symbolization, and production discipline.
Six questions that cut across the whole unit. Each one mirrors a decision you make in a real latency incident — not a definition to recite, but which profile to pull, how to read it, and what its numbers actually mean under production load.
Confirm you can connect sampling economics, profile-type selection, flame-graph reading, eBPF symbolization, and production discipline — the synthesis the individual lessons built toward.
A request takes 500 ms wall-clock but the CPU profile attributes only 20 ms to it. Where did the other 480 ms go, and which profile reveals it?
A service makes 5 million function calls/second. You want always-on production profiling. Why is a sampling profiler the only viable choice over instrumentation?
An engineer points at two wide frames side by side at the same level of a flame graph and concludes the left one runs before the right one. What is wrong?
An eBPF profiler shows clean stacks for Go and Rust services but many '[unknown]' frames for a Python service on the same node. Why?
A continuous profiler is advertised at 2-5% overhead, but you measure 12% in production. What is the most likely cause to check first?
During an incident review someone proposes attaching the production profile to the vendor support ticket. Why should a senior engineer object?
The unit’s through-line is one diagnostic loop: pick the profile that answers your question (CPU for compute, off-CPU/block/mutex for waiting, heap/allocation for memory), read the flame graph correctly (width is sample share, x-axis is alphabetical not time), and trust the numbers only when you know their limits (sampling is bounded but blind to sub-interval hot paths, eBPF needs language-aware symbolization, 2-5% overhead is real but config-sensitive). And because a profile exposes code internals, you treat it as a security-sensitive artefact, not a freely shareable metric.
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