Writing benchmarks¶

Running benchmarks during development¶

There are some options to asv run that may be useful when writing benchmarks.

You may find that asv run spends a lot of time setting up the environment each time. You can have asv run use an existing Python environment that already has the benchmarked project and all of its dependencies installed. Use the --python argument to specify a Python environment to use:

asv run --python=python

If you don’t care about getting accurate timings, but just want to ensure the code is running, you can add the --quick argument, which will run each benchmark only once:

asv run --quick

In order to display the standard error output (this includes exception tracebacks) that your benchmarks may produce, pass the --show-stderr flag:

asv run --show-stderr

Finally, there is a special command, asv dev, that uses all of these features and is equivalent to:

asv run --python=same --quick --show-stderr --dry-run

Setup and teardown functions¶

If initialization needs to be performed that should not be included in the timing of the benchmark, include that code in a setup method on the class, or add an attribute called setup to a free function.

For example:

class Suite:
    def setup(self):
        # load data from a file
        with open("/usr/share/words.txt", "r") as fd:
            self.words = fd.readlines()

    def time_upper(self):
        for word in self.words:
            word.upper()

# or equivalently...

words = []
def my_setup():
    global words
    with open("/usr/share/words.txt", "r") as fd:
        words = fd.readlines()

def time_upper():
    for word in words:
        word.upper()
time_upper.setup = my_setup

You can also include a module-level setup function, which will be run for every benchmark within the module, prior to any setup assigned specifically to each function.

Similarly, benchmarks can also have a teardown function that is run after the benchmark. This is useful if, for example, you need to clean up any changes made to the filesystem.

Note that although different benchmarks run in separate processes, for a given benchmark repeated measurement (cf. repeat attribute) and profiling occur within the same process. For these cases, the setup and teardown routines are run multiple times in the same process.

If setup raises a NotImplementedError, the benchmark is marked as skipped.

The setup method is run multiple times, for each benchmark and for each repeat. If the setup is especially expensive, the setup_cache method may be used instead, which only performs the setup calculation once and then caches the result to disk. It is run only once also for repeated benchmarks and profiling, unlike setup. setup_cache can persist the data for the benchmarks it applies to in two ways:

• Returning a data structure, which asv pickles to disk, and then loads and passes it as the first argument to each benchmark.
• Saving files to the current working directory (which is a temporary directory managed by asv) which are then explicitly loaded in each benchmark process. It is probably best to load the data in a setup method so the loading time is not included in the timing of the benchmark.

A separate cache is used for each environment and each commit of the project begin tested and is thrown out between benchmark runs.

For example, caching data in a pickle:

class Suite:
    def setup_cache(self):
        fib = [1, 1]
        for i in range(100):
            fib.append(fib[-2] + fib[-1])
        return fib

    def track_fib(self, fib):
        return fib[-1]

As another example, explicitly saving data in a file:

class Suite:
    def setup_cache(self):
        with open("test.dat", "wb") as fd:
            for i in range(100):
                fd.write('{0}\n'.format(i))

    def setup(self):
        with open("test.dat", "rb") as fd:
            self.data = [int(x) for x in fd.readlines()]

    def track_numbers(self):
        return len(self.data)

The setup_cache timeout can be specified by setting the .timeout attribute of the setup_cache function. The default value is the maximum of the timeouts of the benchmarks using it.

Benchmark attributes¶

Each benchmark can have a number of arbitrary attributes assigned to it. The attributes that asv understands depends on the type of benchmark and are defined below. For free functions, just assign the attribute to the function. For methods, include the attribute at the class level. For example, the following are equivalent:

def time_range():
    for i in range(1000):
        pass
time_range.timeout = 120.0

class Suite:
    timeout = 120.0

    def time_range(self):
        for i in range(1000):
            pass

For the list of attributes, see Benchmark types and attributes.

Parameterized benchmarks¶

You might want to run a single benchmark for multiple values of some parameter. This can be done by adding a params attribute to the benchmark object:

def time_range(n):
   for i in range(n):
       pass
time_range.params = [0, 10, 20, 30]

This will also make the setup and teardown functions parameterized:

class Suite:
    params = [0, 10, 20]

    def setup(self, n):
        self.obj = range(n)

    def teardown(self, n):
        del self.obj

    def time_range_iter(self, n):
        for i in self.obj:
            pass

If setup raises a NotImplementedError, the benchmark is marked as skipped for the parameter values in question.

The parameter values can be any Python objects. However, it is often best to use only strings or numbers, because these have simple unambiguous text representations.

When you have multiple parameters, the test is run for all of their combinations:

def time_ranges(n, func_name):
    f = {'range': range, 'arange': numpy.arange}[func_name]
    for i in f(n):
        pass

time_ranges.params = ([10, 1000], ['range', 'arange'])

The test will be run for parameters (10, 'range'), (10, 'arange'), (1000, 'range'), (1000, 'arange').

You can also provide informative names for the parameters:

time_ranges.param_names = ['n', 'function']

These will appear in the test output; if not provided you get default names such as “param1”, “param2”.

Note that setup_cache is not parameterized.

Benchmark types¶

class Suite:
    def setup(self):
        # load data from a file
        with open("/usr/share/words.txt", "r") as fd:
            self.words = fd.readlines()

    def time_upper(self):
        for word in self.words:
            word.upper()

def mem_list():
    return [0] * 256

def peakmem_list():
    [0] * 165536

import gc

def track_num_objects():
    return len(gc.get_objects())
track_num_objects.unit = "objects"