Profiling

CIDER has a simple built-in profiler that can help you to quickly measure the running time of individual functions. It is similar to wrapping your functions with time macro, except it records every timing and displays a summarized result.

Profiling is different from benchmarking. Benchmarking more accurately tells you how long the code executes. If you need accurate timing results, use a serious benchmarking library like Criterium. If you need to understand where most of the time is spent, use a serious profiler like clj-async-profiler.
The profiler doesn’t support ClojureScript.

Usage

To start using CIDER profiler, choose the vars you want to profile and invoke M-x cider-profile-toggle (C-c C-= t). By defaults it operates on the symbol at point, but will prompt for a var if there’s nothing under the point. You can also mark all functions in the namespace for profiling via cider-profile-ns-toggle (C-c C-= n).

Then, evaluate some code making use of those vars and their invocations will be automatically profiled.

You can display a report of the collected profiling data with M-x cider-profile-summary (C-c C-= s).

Understanding the Report Format

Profiling reports are rendered by CIDER inspector. A typical profiling report looks like this:

| # |           :name |   :n |  :mean |    :std |   :sum |   :min |   :max |   :med |   :samples |
|---+-----------------+------+--------+---------+--------+--------+--------+--------+------------|
| 0 | #'sample-ns/bar | 1000 |   3 us |  ±14 us |   3 ms | 791 ns | 384 us |   2 us |  [791 ...] |
| 1 | #'sample-ns/baz | 1000 | 307 ns | ±710 ns | 307 us |  84 ns |  22 us | 250 ns |   [84 ...] |
| 2 | #'sample-ns/foo | 1000 |   7 us |  ±18 us |   7 ms |   3 us | 495 us |   5 us | [2584 ...] |
| 3 | #'sample-ns/qux | 1000 |   8 us |  ±20 us |   8 ms |   3 us | 543 us |   5 us | [3125 ...] |

Let’s demystify all the column names:

  • :n: Number of samples.

  • :mean: Average time spent in fn.

  • :std: Standard deviation.

  • :sum: Aggregate time spent in fn.

  • :min: Minimal recorded time for fn.

  • :max: Maximal recorded time for fn.

  • :med: Median i.e. fiftieth percentile.

  • :samples: A list of all timing samples. You can click it to see the full list in the inspector.

Keybindings

Command Keyboard shortcut Description

cider-profile-toggle

C-c C-= t

Toggle profiling for var. Defaults to the var at point.

cider-profile-ns-toggle

C-c C-= n

Toggle profiling for the current ns.

cider-profile-summary

C-c C-= s

Display the profiling summary for all vars.

cider-profile-clear

C-c C-= c

Clear profiling data.