doc: move benchmark/README.md to doc/guides

Since benchmark/README.md is in fact a guide on how to
write and run benchmarks, move it to doc/guides.

PR-URL: https://github.com/nodejs/node/pull/11237
Fixes: https://github.com/nodejs/node/issues/11190
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Andreas Madsen <amwebdk@gmail.com>

3 files changed, 417 insertions, 0 deletions

diff --git a/doc/guides/doc_img/compare-boxplot.png b/doc/guides/doc_img/compare-boxplot.png
new file mode 100644
index 0000000000..2a198a4491
--- /dev/null
+++ b/doc/guides/doc_img/compare-boxplot.png
diff --git a/doc/guides/doc_img/scatter-plot.png b/doc/guides/doc_img/scatter-plot.png
new file mode 100644
index 0000000000..de5358d575
--- /dev/null
+++ b/doc/guides/doc_img/scatter-plot.png
diff --git a/doc/guides/writing-and-running-benchmarks.md b/doc/guides/writing-and-running-benchmarks.md
new file mode 100644
index 0000000000..d123347075
--- /dev/null
+++ b/doc/guides/writing-and-running-benchmarks.md
@@ -0,0 +1,417 @@
+# Node.js core benchmark
+
+This folder contains benchmarks to measure the performance of the Node.js APIs.
+
+## Table of Content
+
+* [Prerequisites](#prerequisites)
+* [Running benchmarks](#running-benchmarks)
+ * [Running individual benchmarks](#running-individual-benchmarks)
+ * [Running all benchmarks](#running-all-benchmarks)
+ * [Comparing node versions](#comparing-node-versions)
+ * [Comparing parameters](#comparing-parameters)
+* [Creating a benchmark](#creating-a-benchmark)
+
+## Prerequisites
+
+Most of the HTTP benchmarks require a benchmarker to be installed, this can be
+either [`wrk`][wrk] or [`autocannon`][autocannon].
+
+`Autocannon` is a Node script that can be installed using
+`npm install -g autocannon`. It will use the Node executable that is in the
+path, hence if you want to compare two HTTP benchmark runs make sure that the
+Node version in the path is not altered.
+
+`wrk` may be available through your preferred package manager. If not, you can
+easily build it [from source][wrk] via `make`.
+
+By default `wrk` will be used as benchmarker. If it is not available
+`autocannon` will be used in it its place. When creating a HTTP benchmark you
+can specify which benchmarker should be used. You can force a specific
+benchmarker to be used by providing it as an argument, e. g.:
+
+`node benchmark/run.js --set benchmarker=autocannon http`
+
+`node benchmark/http/simple.js benchmarker=autocannon`
+
+Basic Unix tools are required for some benchmarks.
+[Git for Windows][git-for-windows] includes Git Bash and the necessary tools,
+which need to be included in the global Windows `PATH`.
+
+To analyze the results `R` should be installed. Check you package manager or
+download it from https://www.r-project.org/.
+
+The R packages `ggplot2` and `plyr` are also used and can be installed using
+the R REPL.
+
+```R
+$ R
+install.packages("ggplot2")
+install.packages("plyr")
+```
+
+### CRAN Mirror Issues
+In the event you get a message that you need to select a CRAN mirror first.
+
+You can specify a mirror by adding in the repo parameter.
+
+If we used the "http://cran.us.r-project.org" mirror, it could look something
+like this:
+
+```R
+install.packages("ggplot2", repo="http://cran.us.r-project.org")
+```
+
+Of course, use the mirror that suits your location.
+A list of mirrors is [located here](https://cran.r-project.org/mirrors.html).
+
+## Running benchmarks
+
+### Running individual benchmarks
+
+This can be useful for debugging a benchmark or doing a quick performance
+measure. But it does not provide the statistical information to make any
+conclusions about the performance.
+
+Individual benchmarks can be executed by simply executing the benchmark script
+with node.
+
+```console
+$ node benchmark/buffers/buffer-tostring.js
+
+buffers/buffer-tostring.js n=10000000 len=0 arg=true: 62710590.393305704
+buffers/buffer-tostring.js n=10000000 len=1 arg=true: 9178624.591787899
+buffers/buffer-tostring.js n=10000000 len=64 arg=true: 7658962.8891432695
+buffers/buffer-tostring.js n=10000000 len=1024 arg=true: 4136904.4060201733
+buffers/buffer-tostring.js n=10000000 len=0 arg=false: 22974354.231509723
+buffers/buffer-tostring.js n=10000000 len=1 arg=false: 11485945.656765845
+buffers/buffer-tostring.js n=10000000 len=64 arg=false: 8718280.70650129
+buffers/buffer-tostring.js n=10000000 len=1024 arg=false: 4103857.0726124765
+```
+
+Each line represents a single benchmark with parameters specified as
+`${variable}=${value}`. Each configuration combination is executed in a separate
+process. This ensures that benchmark results aren't affected by the execution
+order due to v8 optimizations. **The last number is the rate of operations
+measured in ops/sec (higher is better).**
+
+Furthermore you can specify a subset of the configurations, by setting them in
+the process arguments:
+
+```console
+$ node benchmark/buffers/buffer-tostring.js len=1024
+
+buffers/buffer-tostring.js n=10000000 len=1024 arg=true: 3498295.68561504
+buffers/buffer-tostring.js n=10000000 len=1024 arg=false: 3783071.1678948295
+```
+
+### Running all benchmarks
+
+Similar to running individual benchmarks, a group of benchmarks can be executed
+by using the `run.js` tool. Again this does not provide the statistical
+information to make any conclusions.
+
+```console
+$ node benchmark/run.js arrays
+
+arrays/var-int.js
+arrays/var-int.js n=25 type=Array: 71.90148040747789
+arrays/var-int.js n=25 type=Buffer: 92.89648382795582
+...
+
+arrays/zero-float.js
+arrays/zero-float.js n=25 type=Array: 75.46208316171496
+arrays/zero-float.js n=25 type=Buffer: 101.62785630273159
+...
+
+arrays/zero-int.js
+arrays/zero-int.js n=25 type=Array: 72.31023859816062
+arrays/zero-int.js n=25 type=Buffer: 90.49906662339653
+...
+```
+
+It is possible to execute more groups by adding extra process arguments.
+```console
+$ node benchmark/run.js arrays buffers
+```
+
+### Comparing node versions
+
+To compare the effect of a new node version use the `compare.js` tool. This
+will run each benchmark multiple times, making it possible to calculate
+statistics on the performance measures.
+
+As an example on how to check for a possible performance improvement, the
+[#5134](https://github.com/nodejs/node/pull/5134) pull request will be used as
+an example. This pull request _claims_ to improve the performance of the
+`string_decoder` module.
+
+First build two versions of node, one from the master branch (here called
+`./node-master`) and another with the pull request applied (here called
+`./node-pr-5135`).
+
+The `compare.js` tool will then produce a csv file with the benchmark results.
+
+```console
+$ node benchmark/compare.js --old ./node-master --new ./node-pr-5134 string_decoder > compare-pr-5134.csv
+```
+
+For analysing the benchmark results use the `compare.R` tool.
+
+```console
+$ cat compare-pr-5134.csv | Rscript benchmark/compare.R
+
+                                                                                      improvement confidence      p.value
+string_decoder/string-decoder.js n=250000 chunk=1024 inlen=1024 encoding=ascii           12.46 %         *** 1.165345e-04
+string_decoder/string-decoder.js n=250000 chunk=1024 inlen=1024 encoding=base64-ascii    24.70 %         *** 1.820615e-15
+string_decoder/string-decoder.js n=250000 chunk=1024 inlen=1024 encoding=base64-utf8     23.60 %         *** 2.105625e-12
+string_decoder/string-decoder.js n=250000 chunk=1024 inlen=1024 encoding=utf8            14.04 %         *** 1.291105e-07
+string_decoder/string-decoder.js n=250000 chunk=1024 inlen=128  encoding=ascii            6.70 %           * 2.928003e-02
+...
+```
+
+In the output, _improvement_ is the relative improvement of the new version,
+hopefully this is positive. _confidence_ tells if there is enough
+statistical evidence to validate the _improvement_. If there is enough evidence
+then there will be at least one star (`*`), more stars is just better. **However
+if there are no stars, then you shouldn't make any conclusions based on the
+_improvement_.** Sometimes this is fine, for example if you are expecting there
+to be no improvements, then there shouldn't be any stars.
+
+**A word of caution:** Statistics is not a foolproof tool. If a benchmark shows
+a statistical significant difference, there is a 5% risk that this
+difference doesn't actually exist. For a single benchmark this is not an
+issue. But when considering 20 benchmarks it's normal that one of them
+will show significance, when it shouldn't. A possible solution is to instead
+consider at least two stars (`**`) as the threshold, in that case the risk
+is 1%. If three stars (`***`) is considered the risk is 0.1%. However this
+may require more runs to obtain (can be set with `--runs`).
+
+_For the statistically minded, the R script performs an [independent/unpaired
+2-group t-test][t-test], with the null hypothesis that the performance is the
+same for both versions. The confidence field will show a star if the p-value
+is less than `0.05`._
+
+The `compare.R` tool can also produce a box plot by using the `--plot filename`
+option. In this case there are 48 different benchmark combinations, thus you
+may want to filter the csv file. This can be done while benchmarking using the
+`--set` parameter (e.g. `--set encoding=ascii`) or by filtering results
+afterwards using tools such as `sed` or `grep`. In the `sed` case be sure to
+keep the first line since that contains the header information.
+
+```console
+$ cat compare-pr-5134.csv | sed '1p;/encoding=ascii/!d' | Rscript benchmark/compare.R --plot compare-plot.png
+
+                                                                               improvement confidence      p.value
+string_decoder/string-decoder.js n=250000 chunk=1024 inlen=1024 encoding=ascii    12.46 %         *** 1.165345e-04
+string_decoder/string-decoder.js n=250000 chunk=1024 inlen=128 encoding=ascii      6.70 %           * 2.928003e-02
+string_decoder/string-decoder.js n=250000 chunk=1024 inlen=32 encoding=ascii       7.47 %         *** 5.780583e-04
+string_decoder/string-decoder.js n=250000 chunk=16 inlen=1024 encoding=ascii       8.94 %         *** 1.788579e-04
+string_decoder/string-decoder.js n=250000 chunk=16 inlen=128 encoding=ascii       10.54 %         *** 4.016172e-05
+...
+```
+
+![compare tool boxplot](doc_img/compare-boxplot.png)
+
+### Comparing parameters
+
+It can be useful to compare the performance for different parameters, for
+example to analyze the time complexity.
+
+To do this use the `scatter.js` tool, this will run a benchmark multiple times
+and generate a csv with the results.
+
+```console
+$ node benchmark/scatter.js benchmark/string_decoder/string-decoder.js > scatter.csv
+```
+
+After generating the csv, a comparison table can be created using the
+`scatter.R` tool. Even more useful it creates an actual scatter plot when using
+the `--plot filename` option.
+
+```console
+$ cat scatter.csv | Rscript benchmark/scatter.R --xaxis chunk --category encoding --plot scatter-plot.png --log
+
+aggregating variable: inlen
+
+chunk     encoding      mean confidence.interval
+   16        ascii 1111933.3           221502.48
+   16 base64-ascii  167508.4            33116.09
+   16  base64-utf8  122666.6            25037.65
+   16         utf8  783254.8           159601.79
+   64        ascii 2623462.9           399791.36
+   64 base64-ascii  462008.3            85369.45
+   64  base64-utf8  420108.4            85612.05
+   64         utf8 1358327.5           235152.03
+  256        ascii 3730343.4           371530.47
+  256 base64-ascii  663281.2            80302.73
+  256  base64-utf8  632911.7            81393.07
+  256         utf8 1554216.9           236066.53
+ 1024        ascii 4399282.0           186436.46
+ 1024 base64-ascii  730426.6            63806.12
+ 1024  base64-utf8  680954.3            68076.33
+ 1024         utf8 1554832.5           237532.07
+```
+
+Because the scatter plot can only show two variables (in this case _chunk_ and
+_encoding_) the rest is aggregated. Sometimes aggregating is a problem, this
+can be solved by filtering. This can be done while benchmarking using the
+`--set` parameter (e.g. `--set encoding=ascii`) or by filtering results
+afterwards using tools such as `sed` or `grep`. In the `sed` case be
+sure to keep the first line since that contains the header information.
+
+```console
+$ cat scatter.csv | sed -E '1p;/([^,]+, ){3}128,/!d' | Rscript benchmark/scatter.R --xaxis chunk --category encoding --plot scatter-plot.png --log
+
+chunk     encoding       mean confidence.interval
+   16        ascii  701285.96           21233.982
+   16 base64-ascii  107719.07            3339.439
+   16  base64-utf8   72966.95            2438.448
+   16         utf8  475340.84           17685.450
+   64        ascii 2554105.08           87067.132
+   64 base64-ascii  330120.32            8551.707
+   64  base64-utf8  249693.19            8990.493
+   64         utf8 1128671.90           48433.862
+  256        ascii 4841070.04          181620.768
+  256 base64-ascii  849545.53           29931.656
+  256  base64-utf8  809629.89           33773.496
+  256         utf8 1489525.15           49616.334
+ 1024        ascii 4931512.12          165402.805
+ 1024 base64-ascii  863933.22           27766.982
+ 1024  base64-utf8  827093.97           24376.522
+ 1024         utf8 1487176.43           50128.721
+```
+
+![compare tool boxplot](doc_img/scatter-plot.png)
+
+## Creating a benchmark
+
+All benchmarks use the `require('../common.js')` module. This contains the
+`createBenchmark(main, configs[, options])` method which will setup your
+benchmark.
+
+The arguments of `createBenchmark` are:
+
+* `main` {Function} The benchmark function,
+  where the code running operations and controlling timers should go
+* `configs` {Object} The benchmark parameters. `createBenchmark` will run all
+  possible combinations of these parameters, unless specified otherwise.
+  Each configuration is a property with an array of possible values.
+  Note that the configuration values can only be strings or numbers.
+* `options` {Object} The benchmark options. At the moment only the `flags`
+  option for specifying command line flags is supported.
+
+`createBenchmark` returns a `bench` object, which is used for timing
+the runtime of the benchmark. Run `bench.start()` after the initialization
+and `bench.end(n)` when the benchmark is done. `n` is the number of operations
+you performed in the benchmark.
+
+The benchmark script will be run twice:
+
+The first pass will configure the benchmark with the combination of
+parameters specified in `configs`, and WILL NOT run the `main` function.
+In this pass, no flags except the ones directly passed via commands
+that you run the benchmarks with will be used.
+
+In the second pass, the `main` function will be run, and the process
+will be launched with:
+
+* The flags you've passed into `createBenchmark` (the third argument)
+* The flags in the command that you run this benchmark with
+
+Beware that any code outside the `main` function will be run twice
+in different processes. This could be troublesome if the code
+outside the `main` function has side effects. In general, prefer putting
+the code inside the `main` function if it's more than just declaration.
+
+```js
+'use strict';
+const common = require('../common.js');
+const SlowBuffer = require('buffer').SlowBuffer;
+
+const configs = {
+  // Number of operations, specified here so they show up in the report.
+  // Most benchmarks just use one value for all runs.
+  n: [1024],
+  type: ['fast', 'slow'],  // Custom configurations
+  size: [16, 128, 1024]  // Custom configurations
+};
+
+const options = {
+  // Add --expose-internals if you want to require internal modules in main
+  flags: ['--zero-fill-buffers']
+};
+
+// main and configs are required, options is optional.
+const bench = common.createBenchmark(main, configs, options);
+
+// Note that any code outside main will be run twice,
+// in different processes, with different command line arguments.
+
+function main(conf) {
+  // You will only get the flags that you have passed to createBenchmark
+  // earlier when main is run. If you want to benchmark the internal modules,
+  // require them here. For example:
+  // const URL = require('internal/url').URL
+
+  // Start the timer
+  bench.start();
+
+  // Do operations here
+  const BufferConstructor = conf.type === 'fast' ? Buffer : SlowBuffer;
+
+  for (let i = 0; i < conf.n; i++) {
+    new BufferConstructor(conf.size);
+  }
+
+  // End the timer, pass in the number of operations
+  bench.end(conf.n);
+}
+```
+
+## Creating HTTP benchmark
+
+The `bench` object returned by `createBenchmark` implements
+`http(options, callback)` method. It can be used to run external tool to
+benchmark HTTP servers.
+
+```js
+'use strict';
+
+const common = require('../common.js');
+
+const bench = common.createBenchmark(main, {
+  kb: [64, 128, 256, 1024],
+  connections: [100, 500]
+});
+
+function main(conf) {
+  const http = require('http');
+  const len = conf.kb * 1024;
+  const chunk = Buffer.alloc(len, 'x');
+  const server = http.createServer(function(req, res) {
+    res.end(chunk);
+  });
+
+  server.listen(common.PORT, function() {
+    bench.http({
+      connections: conf.connections,
+    }, function() {
+      server.close();
+    });
+  });
+}
+```
+
+Supported options keys are:
+* `port` - defaults to `common.PORT`
+* `path` - defaults to `/`
+* `connections` - number of concurrent connections to use, defaults to 100
+* `duration` - duration of the benchmark in seconds, defaults to 10
+* `benchmarker` - benchmarker to use, defaults to
+`common.default_http_benchmarker`
+
+[autocannon]: https://github.com/mcollina/autocannon
+[wrk]: https://github.com/wg/wrk
+[t-test]: https://en.wikipedia.org/wiki/Student%27s_t-test#Equal_or_unequal_sample_sizes.2C_unequal_variances
+[git-for-windows]: http://git-scm.com/download/win