buffer: optimize Buffer.byteLength #1713

brendanashworth · 2015-05-16T03:42:12Z

Buffer.byteLength is called whenever a new string Buffer is created.
UTF8 is used as the default encoding, and base64 is also popular. These
must be fast and take up a relatively significant part of Buffer
instantiation.

This commit moves the Buffer.byteLength calculations into only JS-land,
moving it from C++ land for base64 and UTF8.

It also adds a benchmark for both encodings; the improvements hover
around 40-60% for UTF8 strings and 170% for base64.

brendanashworth · 2015-05-16T03:49:52Z

benchmark/buffers/buffer-bytelength-utf8.js

+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    Buffer.byteLength(str, 'utf8');


utf8 is passed explicitly as the encoding because there isn't a default encoding in byteLength. utf8 is picked as the default Buffer encoding here, though.

This should probably be modified so that str is different for every iteration of the loop. Otherwise the JIT will most likely "overly optimize" execution because it's seeing the exact same input every time, which may not give reliable/accurate benchmark results.

Good tip - would a few strings (like 4) work? I think that if they were generated newly for each run of the loop it'd take up the majority of the runtime.

Probably just cycling through each of the 4 strings you already have defined would probably work.

sweet, I'll do that + the mixed one, writing a patch

brendanashworth · 2015-05-16T06:46:27Z

Pushed up a patch @mscdex, the benchmark numbers now sit comfortably at 150-330%.

Also, should I default the JS encoding to utf8 since it does it in the C++? It looks like it interacts with a v8 API that I'm not familiar with though so I'm unsure.

brendanashworth · 2015-05-16T07:08:37Z

New findings: ParseEncoding belongs to node and the only format it parses that isn't parsed by byteLength (JS) is base64. I may remove the parseEncoding call altogether, set the default to utf8 in JS, that way it'll optimize a base64 length call too.

petkaantonov · 2015-05-16T07:31:30Z

benchmark/buffers/buffer-bytelength-utf8.js

+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    Buffer.byteLength(chars[0], 'utf8');


Can you add guards to these? E.g. if (Buffer.byteLength(chars[0], 'utf8') !== 16) throw ...

Sure, I'll add a mini-test in the beginning, outside the loop.

I mean inside the loop to avoid unrealistic optimizations, byteLength looks simplistic enough that v8 could determine it's a pure function if not now then in the future

Alright, I'll do some assert()s. :)

In this new commit I'm pushing up, I've changed the benchmark a little bit, and it now has 8 different possibilities for each run in the loop. I'm unsure whether asserting in-loop is still the best choice.

The meaning of the guards is not to be a test but to make the benchmark less susceptible to irrelevant optimizations like licm and dce. There is no reason to use assert and the checks must be done in the loop, otherwise they are ineffective.

brendanashworth · 2015-05-16T21:50:33Z

Force pushed a commit:

add base64 byte length calculation in JS
remove process.binding calls entirely, mimicking the C++ behavior
style fixes (thanks @bnoordhuis)
benchmark strings more spread out (thanks @mscdex)
handle case-insensitive encoding names in JS (ugh backwards compatibility)

I added a note in node_buffer.cc about how ByteLength is not called from JS. Can the function be removed? Is it able to be called from C++ APIs?

Also, pending @petkaantonov's feedback on ensuring the functionality works correctly in the benchmark.

I think the function is now polymorphic in the benchmark or something, because the UTF8 benchmark numbers have dropped somewhat significantly. The base64 is looking great though:

encoding=utf8 len=4: bleed: 4045000 iojs: 2525900 ....... 60.14%
encoding=utf8 len=16: bleed: 4064900 iojs: 2929400 ...... 38.76%
encoding=utf8 len=64: bleed: 4057000 iojs: 2886500 ...... 40.55%
encoding=utf8 len=256: bleed: 4102100 iojs: 2895900 ..... 41.65%
encoding=utf8 len=1024: bleed: 4084700 iojs: 2849100 .... 43.37%
encoding=base64 len=4: bleed: 4074900 iojs: 1537400 .... 165.05%
encoding=base64 len=16: bleed: 4191600 iojs: 1532200 ... 173.57%
encoding=base64 len=64: bleed: 4128100 iojs: 1471200 ... 180.60%
encoding=base64 len=256: bleed: 4119900 iojs: 1535500 .. 168.30%
encoding=base64 len=1024: bleed: 4190700 iojs: 1535700 . 172.89%

bnoordhuis · 2015-05-16T21:58:24Z

benchmark/buffers/buffer-bytelength.js

+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    Buffer.byteLength(chars[n % 4], encoding);


If you change the utf8 and base64 objects to arrays, you can replace the hard-coded constant with n % inputs.length.

brendanashworth · 2015-05-17T02:28:17Z

Pushed another commit, removing the node_buffer::ByteLength function, optimizing away from toLowerCase() calls, and making the benchmark better (thanks @petkaantonov and @bnoordhuis). The benchmark for base64 now says the new implementation is a lot faster, but now I'm struggling to keep larger UTF8 strings (256 characters and above) to be faster in the JS implementation. Smaller strings are still faster.

encoding=utf8 len=1: bleed: 5711000 iojs: 2265700 ... 152.06%
encoding=utf8 len=2: bleed: 3900500 iojs: 2028200 .... 92.32%
encoding=utf8 len=4: bleed: 2538000 iojs: 1669100 .... 52.05%
encoding=utf8 len=16: bleed: 808850 iojs: 979290 .... -17.40%
encoding=utf8 len=64: bleed: 219440 iojs: 370360 .... -40.75%
encoding=base64 len=1: bleed: 5886000 iojs: 1149100 . 412.24%
encoding=base64 len=2: bleed: 5993400 iojs: 1155800 . 418.54%
encoding=base64 len=4: bleed: 5750000 iojs: 1157100 . 396.94%
encoding=base64 len=16: bleed: 6203100 iojs: 929540 . 567.33%
encoding=base64 len=64: bleed: 5916100 iojs: 955250 . 519.33%

Maybe someone has a tip for the UTF8 function?

Previously, there were very few direct tests for Buffer.byteLength(). I realized I had introduced some breaking changes in nodejs#1713 that the tests didn't catch, so I've pretty much added almost every possible corner of the code here. It also takes any other byteLength tests from test-buffer and moves them.

brendanashworth · 2015-05-17T03:15:29Z

Shoot, just realized the new UTF8 parser introduces some breaking changes not covered by the test suite. I'll PR / add a new commit to this PR with the new tests and figure out that darn function 😄

bnoordhuis · 2015-05-17T11:42:02Z

lib/buffer.js

+
+      // Handle uppercased encodings
+      if (encoding !== encoding.toLowerCase())
+        return byteLength(string, encoding.toLowerCase());


Can I suggest you cache the value of encoding.toLowerCase() here, to avoid calling it twice?

Aside: I'm not sure if we have guidelines on whether or not recursion is allowed. I made Buffer#write() iterative instead of recursive to avoid a (probably academic) stack overflow exception when it's getting called when the stack is almost full.

I've cached the output. Would you like me to switch to a loop, like you did?

If nothing else, it'd be consistent with what Buffer#write() does.

Okay, sounds good, I'll make the change.

Buffer.byteLength is called whenever a new string Buffer is created. UTF8 is used as the default encoding, and base64 is also popular. These must be fast and take up a relatively significant part of Buffer instantiation. This commit moves the Buffer.byteLength calculations into only JS-land, moving it from C++ land for base64 and UTF8. It also removes the ByteLength function on the C++ Buffer. It also adds a benchmark for both encodings; the improvements hover for UTF8, change a lot, but base64 is about

brendanashworth · 2015-05-18T05:46:23Z

lib/buffer.js

+      case 'binary':
+      // Deprecated
+      case 'raw':
+      case 'raws':


This was supported by the C++ version, but isn't currently supported by Buffer.isEncoding.

FWIW, I think 'raw' and 'raws' have been deprecated since v0.2 or v0.3. I've never seen them being used in the wild either.

I can follow this PR up with a deprecation commit (to keep it semver-patch) - technically speaking only raws was deprecated, not raw, for this function:

> Buffer.byteLength('abc', 'raw') 3 > Buffer.byteLength('abc', 'raws') 'raws' encoding has been renamed to 'binary'. Please update your code. 3

brendanashworth · 2015-05-18T05:54:58Z

OKAY! I think I got it this time. I've added a relatively large test suite (because it was pretty much not tested before), improved the base64 a little bit, and completely ditched the UTF8 length function. (it is very hard to calculate the length when v8 uses UTF16 on strings and says a 4 byte character is 2 3 byte chars, all the while beating C++). I've instead opted to optimize out some calculations in the C++ side to only give the ->Utf8Length() of the string, yielding some pretty fair perf increases all around, though they kind of go away as the size increases.

encoding=utf8 len=1: bleed: 9909300 iojs: 3971800 ..... 149.49%
encoding=utf8 len=2: bleed: 7524900 iojs: 3583800 ..... 109.97%
encoding=utf8 len=4: bleed: 5155400 iojs: 2907300 ...... 77.32%
encoding=utf8 len=16: bleed: 2261600 iojs: 1757700 ..... 28.67%
encoding=utf8 len=64: bleed: 709970 iojs: 668300 ........ 6.23%
encoding=utf8 len=256: bleed: 195430 iojs: 198300 ...... -1.44%
encoding=base64 len=1: bleed: 9585300 iojs: 2248500 ... 326.31%
encoding=base64 len=2: bleed: 8675000 iojs: 2197100 ... 294.83%
encoding=base64 len=4: bleed: 8766100 iojs: 2191400 ... 300.03%
encoding=base64 len=16: bleed: 8791800 iojs: 1772700 .. 395.96%
encoding=base64 len=64: bleed: 9025300 iojs: 1777600 .. 407.73%
encoding=base64 len=256: bleed: 8777600 iojs: 1195800 . 634.05%

petkaantonov · 2015-05-18T05:58:08Z

src/node_buffer.cc

-  Local<String> s = args[0]->ToString(env->isolate());
-  enum encoding e = ParseEncoding(env->isolate(), args[1], UTF8);
+  // Fast case: avoid StringBytes on UTF8 string. Jump to v8.
+  Local<String> str = args[0]->ToString(env->isolate());


It's guaranteed to be a string so args[0].As<String>(); should be used

Can I drop the Environment::GetCurrent above then, or must that be kept?

Yea the string check and env can be dropped, this is always called with a string from js.

I would leave in a CHECK(args[0]->IsString()) to catch bugs.

bnoordhuis · 2015-05-18T10:38:25Z

src/node_buffer.cc


-  uint32_t size = StringBytes::Size(env->isolate(), s, e);
-  args.GetReturnValue().Set(size);
+  args.GetReturnValue().Set(len);
 }


I think you can reduce this function to just:

void ByteLengthUtf8(const FunctionCallbackInfo<Value>& args) { CHECK(args[0]->IsString()); args.GetReturnValue().Set(args[0].As<String>()->Utf8Length()); }

EDIT: s/UTF8/Utf8/ for consistency with other functions/types operating on UTF-8.

trevnorris · 2015-05-18T19:36:10Z

Looks alright to me. Will the new base64ByteLength() possibly over allocate like the previous implementation does?

brendanashworth · 2015-05-19T02:12:09Z

@trevnorris I don't think so. I used the old algorithm as reference, and the new one doesn't include the extra bytes like the old one did. Otherwise, they're almost the same algorithm.

trevnorris · 2015-05-19T18:39:02Z

lib/buffer.js

-  if (typeof(string) !== 'string')
-    string = String(string);
+  if (typeof string !== 'string')
+    string = '' + string;


Is this a change in functionality? ByteLength() would throw if a non string was passed.

Nope, String(val) also does coercion. We seem to prefer '' + val though.

@bnoordhuis do we care if node aborts if someone does:

process.binding('buffer').byteLengthUtf8(42);

Or do we want to continue throwing?

I don't think so. Fooling around with process.binding() voids the warranty.

trevnorris · 2015-05-19T20:40:26Z

Had my last question confirmed by @bnoordhuis. LGTM.

brendanashworth · 2015-05-19T21:10:03Z

@trevnorris Thanks!

The original CI is mostly out of date. Should I re-run it?

Fishrock123 · 2015-05-19T21:11:24Z

@brendanashworth yes please.

brendanashworth · 2015-05-19T21:15:08Z

Latest CI: https://jenkins-iojs.nodesource.com/job/iojs+any-pr+multi/695/

brendanashworth · 2015-05-19T23:30:03Z

The failures on Windows / ARM / Centos 5 look unrelated, the CI is otherwise happy.

brendanashworth · 2015-05-20T00:11:22Z

As the PR stands, for the respective UTF8 and Base64 hello, world! Buffer creations:

# this PR
utf8 x 2,208,160 ops/sec ±0.75% (93 runs sampled)
base64 x 1,881,927 ops/sec ±0.73% (93 runs sampled)
# v2.0.1
utf8 x 1,502,424 ops/sec ±1.10% (95 runs sampled)
base64 x 969,291 ops/sec ±0.75% (95 runs sampled)
# v0.10.38
utf8 x 659,515 ops/sec ±0.37% (99 runs sampled)
base64 x 408,662 ops/sec ±0.53% (97 runs sampled)

bnoordhuis · 2015-05-20T10:19:26Z

test/parallel/test-buffer-bytelength.js

+assert.equal(Buffer.byteLength('aGVsbG8gd29ybGQ=', 'base64'), 11);
+assert.equal(Buffer.byteLength('bm9kZS5qcyByb2NrcyE=', 'base64'), 14);
+assert.equal(Buffer.byteLength('aGkk', 'base64'), 3);
+assert.equal(Buffer.byteLength('bHNrZGZsa3NqZmtsc2xrZmFqc2RsZmtqcw==', 'base64'), 25);


bnoordhuis · 2015-05-20T10:21:57Z

LGTM with a style nit.

brendanashworth · 2015-05-21T05:52:07Z

Thanks @bnoordhuis, I shall merge in the morning.

Buffer.byteLength is important for speed because it is called whenever a new Buffer is created from a string. This commit optimizes Buffer.byteLength execution by: - moving base64 length calculation into JS-land, which is now much faster - remove redundant code and streamline the UTF8 length calculation It also adds a benchmark and better tests. PR-URL: #1713 Reviewed-By: Trevor Norris <trev.norris@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

brendanashworth · 2015-05-22T22:37:18Z

Thank you reviewers! Landed in 9da168b. (I had to push up a small commit to fix a new failure on HEAD).

Buffer.byteLength is important for speed because it is called whenever a new Buffer is created from a string. This commit optimizes Buffer.byteLength execution by: - moving base64 length calculation into JS-land, which is now much faster - remove redundant code and streamline the UTF8 length calculation It also adds a benchmark and better tests. PR-URL: nodejs/node#1713 Reviewed-By: Trevor Norris <trev.norris@gmail.com> Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

brendanashworth added the buffer Issues and PRs related to the buffer subsystem. label May 16, 2015

brendanashworth reviewed May 16, 2015
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petkaantonov reviewed May 16, 2015
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brendanashworth force-pushed the optimize/new-buffer branch from 1278515 to cb04c10 Compare May 16, 2015 21:45

bnoordhuis reviewed May 16, 2015
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brendanashworth force-pushed the optimize/new-buffer branch from cb04c10 to f6299c4 Compare May 17, 2015 02:23

bnoordhuis reviewed May 17, 2015
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brendanashworth force-pushed the optimize/new-buffer branch from f6299c4 to 7b5655c Compare May 17, 2015 23:02

brendanashworth added 5 commits May 17, 2015 16:40

use loop over recursion, fix tests over binary operator

447fe0b

add a 4096 size string

35eeaea

remove JS utf8 function, optimize for UTF8 with v8

30dea88

make better byteLength tests

69c0889

avoid Math.floor with binary operation

3c05601

brendanashworth reviewed May 18, 2015
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petkaantonov reviewed May 18, 2015
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use charCodeAt() and modifiable arguments

84bb8a4

bnoordhuis reviewed May 18, 2015
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brendanashworth added 2 commits May 18, 2015 06:56

rename function and reduce code size

5156d31

newline at end of file

47a5209

brendanashworth added the c++ Issues and PRs that require attention from people who are familiar with C++. label May 18, 2015

trevnorris reviewed May 19, 2015
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bnoordhuis reviewed May 20, 2015
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fix line length

2f1d3b5

add use strict declaration

0610eb8

brendanashworth closed this May 22, 2015

rvagg mentioned this pull request May 23, 2015

Release proposal v2.1.0 #1777

Closed

ChALkeR added the performance Issues and PRs related to the performance of Node.js. label Feb 16, 2016

buffer: optimize Buffer.byteLength #1713

buffer: optimize Buffer.byteLength #1713

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