# NumPy benchmarks

Benchmarking NumPy with Airspeed Velocity.

## Usage

Airspeed Velocity manages building and Python virtualenvs by itself, unless told otherwise. Some of the benchmarking features in `runtests.py` also tell ASV to use the NumPy compiled by `runtests.py`. To run the benchmarks, you do not need to install a development version of NumPy to your current Python environment.

Before beginning, ensure that airspeed velocity is installed. By default, asv ships with support for anaconda and virtualenv:

    pip install asv
    pip install virtualenv

After contributing new benchmarks, you should test them locally before submitting a pull request.

To run all benchmarks, navigate to the root NumPy directory at the command line and execute:

    python runtests.py --bench

where `--bench` activates the benchmark suite instead of the test suite. This builds NumPy and runs all available benchmarks defined in `benchmarks/`. (Note: this could take a while. Each benchmark is run multiple times to measure the distribution in execution times.)

To run benchmarks from a particular benchmark module, such as `bench_core.py`, simply append the filename without the extension:

    python runtests.py --bench bench_core

To run a benchmark defined in a class, such as `Mandelbrot` from `bench_avx.py`:

    python runtests.py --bench bench_avx.Mandelbrot

Compare change in benchmark results to another version/commit/branch:

    python runtests.py --bench-compare v1.6.2 bench_core
    python runtests.py --bench-compare 8bf4e9b bench_core
    python runtests.py --bench-compare main bench_core

All of the commands above display the results in plain text in the console, and the results are not saved for comparison with future commits. For greater control, a graphical view, and to have results saved for future comparison you can run ASV commands (record results and generate HTML):

    cd benchmarks
    asv run -n -e --python=same
    asv publish
    asv preview

More on how to use `asv` can be found in ASV documentation Command-line help is available as usual via `asv --help` and `asv run --help`.

## Writing benchmarks

See ASV documentation for basics on how to write benchmarks.

Some things to consider:

- The benchmark suite should be importable with any NumPy version.

- The benchmark parameters etc. should not depend on which NumPy version is installed.

- Try to keep the runtime of the benchmark reasonable.

- Prefer ASV’s `time_` methods for benchmarking times rather than cooking up time measurements via `time.clock`, even if it requires some juggling when writing the benchmark.

- Preparing arrays etc. should generally be put in the `setup` method rather than the `time_` methods, to avoid counting preparation time together with the time of the benchmarked operation.

- Be mindful that large arrays created with `np.empty` or `np.zeros` might not be allocated in physical memory until the memory is accessed. If this is desired behaviour, make sure to comment it in your setup function. If you are benchmarking an algorithm, it is unlikely that a user will be executing said algorithm on a newly created empty/zero array. One can force pagefaults to occur in the setup phase either by calling `np.ones` or `arr.fill(value)` after creating the array,

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