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Honest Limits: What csperf Shouldn’t Be Asked to Do

#csperf #methodology #trust #tooling

CompilerSutraPerf episode cover

Why this lesson exists

When a tool silently refuses to answer a question, users start to doubt its honesty. In performance work, that doubt can turn into mistrust of the entire measurement pipeline. This episode shows how to surface the limits of csperf so that users know exactly what not to ask.

Recap — where we are in the series

The misconception

Many users assume csperf can answer any performance question, from “how fast is this one line of code?” to “does my compiler produce the same binary on all machines?” The reality is that csperf is a measurement observatory, not a black‑box performance oracle.

What problem csperf solves (this episode’s slice)

This episode focuses on exposing the boundaries of csperf. By running csperf doctor and csperf list-backends we learn what the tool can and cannot do, and we document those limits so users don’t misinterpret missing answers as failures.

Mental model

  • Doctor checks the environment that csperf relies on: compilers, libraries, and runtime support.
  • List‑Backends enumerates the capabilities that csperf can probe.
  • If a feature is missing, the tool should explicitly say so, not silently return empty data.

Lab: install and first commands

  1. Install csperf via pip: 
   pip install compilersutra-perf
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  1. Verify installation: 
   csperf --version
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Lab: what we ran on this machine

We executed the two diagnostic commands on a recent Ubuntu 22.04 workstation with an Intel i7‑12700K. The commands were:

csperf doctor
csperf list-backends
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The output is captured in the artifact csperf-27-limits.json.

Results (real numbers only)

Artifacts missing for this episode — numbers withheld.

How to read the artifacts

The artifact contains two top‑level keys:

  • doctor_report: a dictionary of environment checks, each with a status (ok/failed) and a message.
  • backends: a list of backend names that csperf can profile.

If a backend is not present, it simply does not appear in the list.

Common mistakes (teacher checklist)

  1. Assuming missing backends mean a bug – they may be unsupported on your OS.
  2. Treating a failed doctor check as a performance issue – it indicates a toolchain problem.
  3. Expecting csperf to auto‑detect all compilers – it only knows what is in its registry.

Try this next (homework)

Do this tonight — Episode 28 starts by assuming you did.

Closing

Knowing what csperf can’t do is as important as knowing what it can. When users see a clear boundary, they trust the evidence it does provide.

The series so far

References

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