Node: Performance degradation in String.prototype.split

[ruimarinho]

• Version: multiple
• Platform: Darwin (macOS)

I've noticed that String.prototype.split's performance has degraded between node versions. Any idea what could be causing this?

| node | ops/sec |
| ------------- |:-------------:|
| 4 | 11,302,467 |
| 6 | 10,896,220 |
| 8 | 8,753,949 |
| 9 | 9,217,843 |

[vsemozhetbyt]

@ruimarinho Could you provide the benchmark code?

cc @nodejs/performance, @nodejs/v8.

[ruimarinho]

Install benchmark:

npm i benchmark

Code:

var Benchmark = require('benchmark');
var suite = new Benchmark.Suite;

suite.add('String#split', function() {
  'FOO-BAR'.split('-');
}).on('cycle', function(event) {
  console.log(String(event.target));
}).run({ async: true });

[vsemozhetbyt]

@ruimarinho I think this is caused by Crankshaft-to-Turbofan transition period. With V8 6.3 and 6.4, the performance is even better than in Node v4 and v6. My results in Windows 7 x64:

Node.js 4  (V8 4.5) String#split x 5,299,950 ops/sec ±0.88% (91 runs sampled)
Node.js 6  (v8 5.1) String#split x 5,747,220 ops/sec ±1.77% (97 runs sampled)
Node.js 8  (v8 6.1) String#split x 4,721,536 ops/sec ±0.56% (99 runs sampled)
Node.js 9  (V8 6.2) String#split x 4,932,482 ops/sec ±0.44% (102 runs sampled)
Node.js 9  (V8 6.3) String#split x 8,058,390 ops/sec ±0.47% (107 runs sampled) // canary build
Node.js 10 (V8 6.4) String#split x 8,067,840 ops/sec ±0.52% (104 runs sampled) // canary build

[vsemozhetbyt]

You can check with these canary builds:

Node.js 9 (V8 6.3)
Node.js 10 (V8 6.4)

[bmeurer]

cc @schuay

[schuay]

Opened https://crbug.com/v8/7103 for possible improvements to String.p.split. There shouldn't be a huge difference between somewhat recent V8 versions, Both the old JS- and new CSA implementation call into Runtime::kStringSplit which is expected to be quite slow in this simple case of short string subject and pattern.

[apapirovski]

There doesn't seem to be much actionable here on Node's part. I'll close this out for now.