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csperf: A Lightweight Observatory for Honest Performance Tracking

#csperf #compilers #performance #tooling

Why this lesson exists

In the first four episodes we learned that a single timing, a single trial, or a screenshot can mislead. We also saw how metadata lets us compare across machines. Yet many teams still rely on bloated CI dashboards that hide noise behind fancy graphs. This episode shows how a tiny, focused observatory—csperf—can give you the same honest evidence without the overhead.

Recap — where we are in the series

  • Ep 1 – Why a Single ./a.out Time Misleads Your Performance Claims: single‑shot timings are unreliable.
  • Ep 2 – Warm vs Cold: Why a Single Trial Misleads Performance Claims: warm‑up and repeat runs are essential.
  • Ep 3 – Screenshots Aren't Evidence: Use csperf for Real Performance Artifacts: screenshots lack reproducibility.
  • Ep 4 – Comparing Across Machines: Why Metadata Matters in csperf: metadata makes cross‑machine comparison honest.

The misconception

Some developers think a small tool like csperf is just a toy or that it can replace full CI pipelines. The truth is that csperf is a tool—not a replacement for CI, but a lightweight observatory that surfaces the raw evidence you need before you build a pipeline.

What problem csperf solves (this episode's slice)

csperf gives you:

  1. A quick sanity check of your environment (csperf doctor).
  2. A list of backends you can run (csperf list-backends).
  3. A machine snapshot (csperf machine.txt) that you can attach to any measurement.

These are the first steps in a disciplined performance workflow.

Mental model

Think of csperf as a weather station for your compiler experiments. It records the temperature (machine state) and wind speed (CPU frequency) before you take a rain gauge (actual measurement). Without the station you can’t tell if a sudden drop in performance is due to a storm or a change in the weather.

Lab: install and first commands

  1. Help – see what the tool can do: 
   csperf --help
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Output shows available sub‑commands and flags.

  1. List backends – discover what you can benchmark: 
   csperf list-backends
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The tool writes csperf/backends.txt and prints the names on stdout.

  1. Doctor – run a sanity check of the environment: 
   csperf doctor
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The tool writes csperf/doctor.txt and exits with 0 if everything looks good.

Lab: what we ran on this machine

We executed the three commands above on a machine with the following snapshot (excerpt from csperf/machine.txt):

hostname=f4c59d864117
CPU(s)=16
Thread(s) per core=2
Core(s) per socket=8
Socket(s)=1
Frequency boost=enabled
CPU scaling MHz=74%
CPU max MHz=5582.3008
CPU min MHz=605.3100
BogoMIPS=7599.98
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The artifact files were written to:

/home/aitr/compilersutra/jenkins_pipeline/artifacts/build-23/csperf/backends.txt
/home/aitr/compilersutra/jenkins_pipeline/artifacts/build-23/csperf/doctor.txt
/home/aitr/compilersutra/jenkins_pipeline/artifacts/build-23/csperf/machine.txt
/home/aitr/compilersutra/jenkins_pipeline/artifacts/build-23/csperf/file-list.txt
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Results (real numbers only)

  • Machine snapshot shows 16 logical CPUs, 8 cores, 2 threads per core, and a 74 % scaling factor.
  • Doctor produced no errors; the exit code was 0.
  • Backends list contains the backends available on this host (the exact names are in backends.txt).

These numbers are the foundation for any subsequent measurement.

How to read the artifacts

File What it contains How to use it
machine.txt Full machine metadata Attach to any measurement to contextualize results
doctor.txt Diagnostic log Verify environment before measurement
backends.txt List of compiler backends Pick a backend for csperf run
file-list.txt Inventory of all artifacts Useful for reproducibility scripts

Open each file in a text editor or less to inspect the raw data.

Common mistakes (teacher checklist)

  1. Skipping csperf doctor – you’ll get noisy data if the environment is mis‑configured.
  2. Assuming csperf list-backends output is exhaustive – it only lists what the tool can find locally.
  3. Ignoring the machine snapshot – without it you can’t compare across runs or machines.
  4. Treating csperf as a full CI replacement – it is an observatory, not a pipeline.

Try this next (homework)

  1. Run csperf doctor again and inspect doctor.txt for any warnings.
  2. Use csperf list-backends to pick a backend you want to benchmark.
  3. Prepare a simple hello.c program and run a measurement with csperf run --backend <name> hello.c.

Do this tonight — Episode 6 starts by assuming you did.

Closing

We have moved from single‑shot timings to a lightweight observatory that records the environment. In the next episode we’ll dive into the first measurement command and see how csperf doctor ensures the data you collect is trustworthy.

The series so far

  • Ep 1 – Why a Single ./a.out Time Misleads Your Performance Claims (this article)
  • Ep 2 – Warm vs Cold: Why a Single Trial Misleads Performance Claims
  • Ep 3 – Screenshots Aren't Evidence: Use csperf for Real Performance Artifacts
  • Ep 4 – Comparing Across Machines: Why Metadata Matters in csperf
  • Ep 5 – csperf: A Lightweight Observatory for Honest Performance Tracking

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