https://github.com/nh2/haskell-cpu-instruction-counter

Measuring CPU instructions in Haskell using Linux Performance Counters
https://github.com/nh2/haskell-cpu-instruction-counter

haskell performance

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Measuring CPU instructions in Haskell using Linux Performance Counters

• Host: GitHub
• URL: https://github.com/nh2/haskell-cpu-instruction-counter
• Owner: nh2
• License: mit
• Created: 2018-02-21T03:18:17.000Z (over 6 years ago)
• Default Branch: master
• Last Pushed: 2018-06-09T14:54:02.000Z (over 6 years ago)
• Last Synced: 2024-04-14T16:06:09.438Z (7 months ago)
• Topics: haskell, performance
• Language: Haskell
• Homepage:
• Size: 11.7 KB
• Stars: 83
• Watchers: 7
• Forks: 5
• Open Issues: 6
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# cpu-instruction-counter

Measuring CPU instructions using Linux Performance Counters / `perf_event_open()`.

Especially useful for writing **performance regression tests**.

Counting CPU instructions counts is a measure of performance that is largely independent of machine/processor types and current load, thus making for more stable benchmarks than measuring wall time or system CPU time.

## Example usage

```haskell

(result, instrs) <- withInstructionsCounted $ do

  return () -- your code here

print (result, instructions)

```

## Example regression test

Put something like this into your CI to get notified about performance regressions in:

* your code

* libraries you use

* code generated by the compiler

```haskell

import           System.CPUInstructionCounter

main :: IO ()

main = do

  (_, sumInstrs) <- withInstructionsCounted $ do

    return $! sum [1..10000::Int]

  let expected = 90651 -- measured on my Core i5-4590, with lts-10.3

  if sumInstrs > (2 * expected)

    then error $ "sum [1..10000] performance regressed; took " ++ show sumInstrs ++ " instructions"

    else putStrLn $ "sum [1..10000] performance OK; took " ++ show sumInstrs ++ " instructions"

```

## Concurrency warning

You will likely not get accurate results when you use `perf_event_open()` in concurrent (e.g. from multiple Haskell threads). See also https://github.com/nh2/haskell-cpu-instruction-counter/issues/4.

You are therefore advised to:

* Disable parallel test running in your testing framework for tests that use CPU counting

## Root permissions

`perf_event_open()` might be restricted on your system. If `cat /proc/sys/kernel/perf_event_paranoid` shows a number greater than `2`, you'll need `sudo` to run the above examples.

Alternatively, run `echo 2 | sudo tee /proc/sys/kernel/perf_event_paranoid`.

By default `perf_event_paranoid` is set to `2` since Linux 4.6 (and before that the default was `1`). Unless your distribution configures it differently you are fine. Ubuntu [is known](https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1612790) to change this setting to `3`.

On CI systems under your control and many public CI services, there should be no barriers to root access so this should not be a showstopper to using this approach for performance regression tests.