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Painless benchmarking with Leiningen 2


Painless benchmarking with Leiningen and Criterium.


Perforate is a plugin for Leiningen 2 that makes it easy to write and run benchmarks, much like the test task built into Leiningen. The benchmarking is done with Hugo Duncan's Criterium, which is carefully designed to overcome common JVM benchmarking pitfalls.

To use perforate, create a directory in your project containing perforate benchmarking source (see simple_bench.clj below). The default directory location is benchmarks/, but you can also specify an alternative location in your project i.e. {:perforate {:benchmark-paths ["src/bench/clojure"]. This directory will be added to the classpath when perforate runs, and all the specified tests inside it will be run. Again, you can think of it as being very similar to the "test/" directory used by the test task.

When you are trying to learn about the performance of some code, you are typically focused on specific tasks or goals that you would like the code to perform. You are also interested in the performance characteristics of one or more different ways of accomplishing that goal. Perforate is organized around these two concepts: goals are the abstract goal that you wish to test various implementations of, while cases are tests of the specific implementations. When you run the perforate task, the report that it generates will group all of the cases in a given goal together to make it easy to compare them.

The perforate.core namespace defines functions and macros that make it easy to define goals and cases. For example, suppose there is a file in benchmarks/myproject/simple_bench.clj:

(ns myproject.simple-bench
  (:use perforate.core))

(defgoal simple-bench "A simple benchmark.")

(defcase simple-bench :really-simple
  [] (+ 1 1))

(defcase simple-bench :slightly-less-simple
  [] (+ 1 1 1))

Here we defined a simple benchmark called simple-bench and gave it a doc string. We also defined two cases, :really-simple and :slightly-less-simple. As you can see, goals are "open" in the sense that you can add as many cases to a given goal as you'd like, or even spread them across namespaces. There is some similarity between defgoal/defcase and defmulti/defmethod.

By default, perforate will run all benchmarks it finds in the "benchmarks/" directory of your project. But you can get much finer control by adding a :perforate key to your project map. The value of this key should be a map. The key :environments will hold a sequence of test environments the plugin should run when it is called. An environment consists of a map of key/value pairs. When present, the :profiles key should be a sequence of profiles from the project.clj that should be merged into the project map during this run of the benchmark. When present, the :namespaces key, should contain a sequence of symbols naming the namespaces to run. You can also add a :name key to give each environment a name. For example, suppose the project.clj file contains the following:

:perforate {:environments [{:name :a1b1
                            :profiles [:a1 :b1]
                            :namespaces [myproject.simple-bench myproject.complex-bench]}
                           {:name :a2b2
                            :profiles [:a2 :b2]
                            :namespaces [myproject.simple-bench myproject.trivial-bench]}]}

As you can see in this example, we have two environments, each using two different profiles. The two environments will run a shared set of benchmarks and a set of benchmarks specific to that environment, perhaps because in the environment inadequate or older versions of libraries are being tested.

Using the environments in combination with Leiningen 2's profiles, you can create sets of tests that run on multiple versions of Clojure, or use older versions of libraries, or use other sets of options from the project map. By naming environments on the command line when you run the perforate task, you can restrict the benchmark run to only the environments you specified.

One thing to note: by default, the source directories are not included on the classpath. This allows you to easily work off of JARs containing old versions of your project just by including them in the dependencies of the profiles you specify. If you want to test the current version from the source directory, just make a profile containing a :source-paths key which contains the "src/" directory (or wherever your source is).

Setup and Cleanup

Many benchmarks require some work to set up the environment in which they run, and some also require cleanup work to remove any byproducts of the tasks being tested or the setup phase itself. You can specify a function to run as a setup (or cleanup) phase by passing it as an argument to defgoal:

(defgoal simple-with-setup "A benchmark with a setup phase."
   :setup (fn [] stuff... [1 2 3])
   :cleanup (fn [a b c] stuff...)

Note how the setup function returns a vector of three values. The cleanup function takes three arguments. When the cleanup function is called (if there is one), it will have the return value of the setup function applied to its arguments. So be sure they match.

The return value of the setup function is also passed to your benchmark function. Thus, it must have a matching set of arguments in the defcase arglists, as shown in the following defcase for simple-with-setup:

(defcase simple-with-setup :default
  [a b c] (+ a b c))

Starting in version 0.3.0, you can also specify clojure.test-style fixtures in your perforate options. Fixtures are useful for setup work that is specific to an environment and not necessarily a goal. For example, your perforate options might look like

  [{:name :array
    :namespaces [myproject.implementation]
    :fixtures [myproject.implementation.array/with-array]}
   {:name :volatile
    :namespaces [myproject.implementation]
    :fixtures [myproject.implementation.type/with-volatile]}
   {:name :unsynchronized
    :namespaces [myproject.implementation]
    :fixtures [myproject.implementation.type/with-unsynchronized]}]}

In this example, the same exact tests are run (those in the namespace myproject.implementation), but the fixtures such as with-array could be something that swaps out the implementation used, as in

(defn with-array [f] 
  (with-redefs [myproject.core/execute-expr-core execute-expr-core-with-array] 

Or perhaps some parameter of interest can be dynamically bound to different values using fixtures, to see how the parameter causes performance to vary. However, this last example illustrates the need for caution when using fixtures: certain dynamic constructs like a dynamic variable, when used in a very tight inner loop function that you are attempting to measure, could result in misleading results. You should probably not reach for fixtures as your first option for running tests, but if they are a good fit, use a little extra caution to make sure you know what you are measuring when you do.

Under the Hood

In reality, the function that gets benchmarked by criterium always takes zero arguments. The defcase macro is doing some work behind the scenes to give you the arglist in lexical scope while still running as a zero-argument function. A case is actually a function that returns the function to be benchmarked. The case function accepts the setup function's arguments, if any, and returns the function to be benchmarked as a closure over the setup function arguments.

Sometimes it's helpful to do some additional case-specific setup on those arguments before returning the actual function to be benchmarked for the given case. For this, there's the lower-level defcase*, which takes a single argument: a function that returns the function to be benchmarked. This function must have an arglist that matches the return value of the setup function, and must return a vector containing either one or two functions. The first function is always the function be benchmarked; if there is a second function, it is a case-specific cleanup function that will be called when that case is done being measured. Here is the simple-with-setup example as a defcase*:

(defcase* simple-with-setup :default2
  (fn [a b c] [(fn [] (+ a b c))]))

As you can see, this function returns the benchmarkable function in a vector, but is otherwise equivalent. In fact, the defcase version should turn into something quite like this defcase* version. The main interest in defcase* is if there is some case-specific setup or cleanup. An example might be

(defcase* simple-with-setup :case-setup
  (fn [a b c] 
    (let [d (* a b c)]
      [(fn [] (+ a b c d))])))

An Example

Suppose the project map contains the following keys:

:dependencies [[org.clojure/clojure "1.3.0"]
               [perforate "0.3.4"]]
  :plugins [[perforate "0.3.4"]]
  :profiles {:current {:source-paths ["src/"]}
             :clj1.4 {:dependencies [[org.clojure/clojure "1.4.0-beta5"]]}
             :clj1.3 {:dependencies [[org.clojure/clojure "1.3.0"]]}
             :version1 {:dependencies [[myproject "1.0.0"]]}
             :version2 {:dependencies [[myproject "2.0.0"]]}}
  :perforate {:environments [{:name :version1
                              :profiles [:clj1.3 :version1]
                              :namespaces [myproject.benchmarks.core]}
                             {:name :version2
                              :profiles [:clj1.3 :version2]
                              :namespaces [myproject.benchmarks.core]}
                             {:name :current
                              :profiles [:clj1.4 :current]
                              :namespaces [myproject.benchmarks.core]}]}

A run could look like this:

David$ lein2 perforate
Benchmarking profiles:  [:clj1.3 :version1]
Goal:  Test Speed
Case: :default
Evaluation count             : 120
             Execution time mean : 793.924842 ms  95.0% CI: (793.842767 ms, 793.975717 ms)
    Execution time std-deviation : 11.865390 ms  95.0% CI: (11.814311 ms, 11.917502 ms)
         Execution time lower ci : 780.498500 ms  95.0% CI: (780.498500 ms, 780.498500 ms)
         Execution time upper ci : 809.372500 ms  95.0% CI: (809.368000 ms, 809.372500 ms)

Benchmarking profiles:  [:clj1.3 :version2]
Goal:  Test Speed
Case: :default
Evaluation count             : 120
             Execution time mean : 637.975817 ms  95.0% CI: (637.931333 ms, 638.011125 ms)
    Execution time std-deviation : 8.807448 ms  95.0% CI: (8.771608 ms, 8.859762 ms)
         Execution time lower ci : 627.351225 ms  95.0% CI: (627.351225 ms, 627.353000 ms)
         Execution time upper ci : 649.712000 ms  95.0% CI: (649.712000 ms, 649.713975 ms)

Benchmarking profiles:  [:clj1.4 :current]
Goal:  Test Speed
Case: :default
Evaluation count             : 120
             Execution time mean : 633.556467 ms  95.0% CI: (633.515842 ms, 633.607392 ms)
    Execution time std-deviation : 9.972554 ms  95.0% CI: (9.914351 ms, 10.055073 ms)
         Execution time lower ci : 622.291500 ms  95.0% CI: (622.291500 ms, 622.291500 ms)
         Execution time upper ci : 647.861000 ms  95.0% CI: (647.861000 ms, 647.887350 ms)

Found 2 outliers in 60 samples (3.3333 %)
    low-severe   2 (3.3333 %)
 Variance from outliers : 1.6389 % Variance is slightly inflated by outliers

If you only wanted to run the :current profile, and you wanted Criterium to do faster, less accurate benchmarks, you could run the following command on the command-line, which would result in similar output:

David$ lein2 perforate current --quick
Benchmarking profiles:  [:clj1.4 :current]
WARNING: Final GC required 3.7433766853457424 % of runtime
WARNING: Final GC required 2.563144804701669 % of runtime
Goal:  Test Speed
Case:  :default
Evaluation count             : 6
             Execution time mean : 524.897667 ms  95.0% CI: (524.493000 ms, 525.080167 ms)
    Execution time std-deviation : 8.663503 ms  95.0% CI: (8.414881 ms, 8.730166 ms)
         Execution time lower ci : 515.172000 ms  95.0% CI: (515.172000 ms, 515.172000 ms)
         Execution time upper ci : 534.102250 ms  95.0% CI: (534.102250 ms, 534.102250 ms)


  • Released version 0.3.4, which fixes a bug that caused goal cleanup to run before the rest of the cases. Thanks to Martin Harrigan for this fix.

  • Released version 0.3.3, which allows configuration of the benchmark source directory and prints more helpful output. Big thanks to Noah Zucker for these improvements.

  • Released version 0.3.2, which updates the version of Criterium used (thus fixing a problem with the previous version attempting to use an incompatible one).

  • Released version 0.3.1, which fixes a bug that prevented defcase from working correctly when the argument list was not empty.

  • Released version 0.3.0, which adds support for outputting benchmark results in new formats: EDN, CSV, and table. Also adds support for fixtures. Thanks to Hugo Duncan.

  • Released version 0.2.4, which updates to the latest version of Criterium and runs all benchmarks with warn-on-reflection set to true.

  • Released version 0.2.3, which updates for latest Leiningen 2 preview versions.

  • Released version 0.2.2, which adds the defcase-fn convenience macro. Should be nicer to use instead of defcase* for cases with no cleanup functions.

  • Released version 0.2.1, which fixes the (previously) completely broken defcase macro.

  • Released version 0.2.0, a substantial redesign and rewrite.

    • Now works without the need to specify environments, thanks to Hugo Duncan.
    • Redesigned to an "open" system modeled on multimethods.
    • Added command line arguments to the perforate task, so specific environments and options can be specified on the command line.
  • Released version 0.1.1 with some bug fixes.



Copyright © 2012 David Santiago

Distributed under the Eclipse Public License, the same as Clojure.

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