Performance is subpar compared to `simdutf::validate_utf8()`

[lpinca]

I've opened websockets/utf-8-validate#109 to use is_utf8 in utf-8-validate.

When running the same benchmarks run in websockets/utf-8-validate#101 I noticed a significant performance drop.

$ npx envinfo --system

  System:
    OS: macOS 13.1
    CPU: (16) x64 Intel(R) Xeon(R) W-2140B CPU @ 3.20GHz
    Memory: 21.54 GB / 32.00 GB
    Shell: 5.2.15 - /usr/local/bin/bash

is_utf8()

$ node bench.js 
Loading https://en.wikipedia.org/wiki/Main_Page ...
utf-8-validate (5.0.10, C++) x 106,808 ops/sec ±0.27% (95 runs sampled)
utf-8-validate (is_utf8, C++) x 105,159 ops/sec ±0.11% (95 runs sampled)
------------------------------------------------------------

Loading https://ro.wikipedia.org/wiki/Pagina_principală ...
utf-8-validate (5.0.10, C++) x 25,410 ops/sec ±0.09% (97 runs sampled)
utf-8-validate (is_utf8, C++) x 54,815 ops/sec ±0.09% (96 runs sampled)
------------------------------------------------------------

Loading https://ru.wikipedia.org/wiki/Заглавная_страница ...
utf-8-validate (5.0.10, C++) x 15,160 ops/sec ±0.10% (98 runs sampled)
utf-8-validate (is_utf8, C++) x 63,985 ops/sec ±0.09% (99 runs sampled)
------------------------------------------------------------

Loading https://ar.wikipedia.org/wiki/الصفحة_الرئيسية ...
utf-8-validate (5.0.10, C++) x 12,766 ops/sec ±0.08% (98 runs sampled)
utf-8-validate (is_utf8, C++) x 57,442 ops/sec ±0.08% (98 runs sampled)
------------------------------------------------------------

Loading https://ja.wikipedia.org/wiki/メインページ ...
utf-8-validate (5.0.10, C++) x 23,306 ops/sec ±0.07% (96 runs sampled)
utf-8-validate (is_utf8, C++) x 79,199 ops/sec ±0.10% (95 runs sampled)
------------------------------------------------------------

Loading https://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt ...
utf-8-validate (5.0.10, C++) x 66,890 ops/sec ±0.10% (99 runs sampled)
utf-8-validate (is_utf8, C++) x 622,514 ops/sec ±0.10% (99 runs sampled)

simdutf::validate_utf8()

$ node bench.js 
Loading https://en.wikipedia.org/wiki/Main_Page ...
utf-8-validate (5.0.10, C++) x 107,373 ops/sec ±0.08% (99 runs sampled)
utf-8-validate (simdutf, C++) x 749,966 ops/sec ±0.20% (96 runs sampled)
------------------------------------------------------------

Loading https://ro.wikipedia.org/wiki/Pagina_principală ...
utf-8-validate (5.0.10, C++) x 25,413 ops/sec ±0.08% (98 runs sampled)
utf-8-validate (simdutf, C++) x 144,119 ops/sec ±0.19% (95 runs sampled)
------------------------------------------------------------

Loading https://ru.wikipedia.org/wiki/Заглавная_страница ...
utf-8-validate (5.0.10, C++) x 15,164 ops/sec ±0.08% (98 runs sampled)
utf-8-validate (simdutf, C++) x 176,840 ops/sec ±0.18% (94 runs sampled)
------------------------------------------------------------

Loading https://ar.wikipedia.org/wiki/الصفحة_الرئيسية ...
utf-8-validate (5.0.10, C++) x 12,781 ops/sec ±0.08% (100 runs sampled)
utf-8-validate (simdutf, C++) x 152,366 ops/sec ±0.16% (97 runs sampled)
------------------------------------------------------------

Loading https://ja.wikipedia.org/wiki/メインページ ...
utf-8-validate (5.0.10, C++) x 23,298 ops/sec ±0.09% (99 runs sampled)
utf-8-validate (simdutf, C++) x 222,036 ops/sec ±0.18% (95 runs sampled)
------------------------------------------------------------

Loading https://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt ...
utf-8-validate (5.0.10, C++) x 66,875 ops/sec ±0.11% (95 runs sampled)
utf-8-validate (simdutf, C++) x 1,051,967 ops/sec ±0.09% (100 runs sampled)

I did not investigate but I think this is because there is no AVX-512 implementation in is_utf8(), right?

[lpinca]

I did not investigate but I think this is because there is no AVX-512 implementation in is_utf8(), right?

Compiling simdutf with SIMDUTF_IMPLEMENTATION_ICELAKE=0 and SIMDUTF_IMPLEMENTATION_WESTMERE=0 produces the same results so I do not think it is that.

[lemire]

Thanks for the report.

[lemire]

Issue verified and reproduced. You are correct, it is not related to AVX-512 at all.

You are also correct that I did not include the AVX-512 kernel: it would be easily done (we have the code already), but if one is concerned by size, it is probably the last kernel to include.

[lemire]

Please upgrade to 1.1.0. I did not want to go down this road, but I ended up doing a direct import of a simdutf, only keeping the validate_utf8 function, manually removing everything else. It is unpleasant, but this is_utf8 library is meant to not ever evolve once settled as it meets a very specific need. It should only do one thing.

You should now have performance parity with simdutf library, down to the AVX-512 kernel. Here are my results on an AWS node:

$ ./build/benchmarks/bench
string size = 40096
basic_validate_utf8   0.293414 GB/s
simdutf               13.321662 GB/s
is_utf8               13.334992 GB/s

string size = 100000
basic_validate_utf8   0.253958 GB/s
simdutf               13.431553 GB/s
is_utf8               13.464450 GB/s

string size = 50000
basic_validate_utf8   0.280539 GB/s
simdutf               13.384315 GB/s
is_utf8               13.378187 GB/s

[lpinca]

I confirm that performance is now the same. Thank you.
I'm not interested in AVX-512 support but the binary size did not grow much (117004 -> 126652 on macOS) so I think it is not a problem.

[lpinca]

There are some warnings.

../deps/is_utf8/src/is_utf8.cpp:568:20: warning: unused variable 'avx512ifma' [-Wunused-const-variable]
constexpr uint32_t avx512ifma = uint32_t(1) << 21;
                   ^
../deps/is_utf8/src/is_utf8.cpp:575:20: warning: unused variable 'avx512vbmi' [-Wunused-const-variable]
constexpr uint32_t avx512vbmi = uint32_t(1) << 1;
                   ^
../deps/is_utf8/src/is_utf8.cpp:577:20: warning: unused variable 'avx512vnni' [-Wunused-const-variable]
constexpr uint32_t avx512vnni = uint32_t(1) << 11;
                   ^
../deps/is_utf8/src/is_utf8.cpp:578:20: warning: unused variable 'avx512bitalg' [-Wunused-const-variable]
constexpr uint32_t avx512bitalg = uint32_t(1) << 12;
                   ^
../deps/is_utf8/src/is_utf8.cpp:579:20: warning: unused variable 'avx512vpopcnt' [-Wunused-const-variable]
constexpr uint32_t avx512vpopcnt = uint32_t(1) << 14;
                   ^
../deps/is_utf8/src/is_utf8.cpp:582:20: warning: unused variable 'avx512vp2intersect' [-Wunused-const-variable]
constexpr uint32_t avx512vp2intersect = uint32_t(1) << 8;
                   ^
../deps/is_utf8/src/is_utf8.cpp:2523:37: warning: unused function 'count_ones' [-Wunused-function]
is_utf8_really_inline long long int count_ones(uint64_t input_num) {
                                    ^
../deps/is_utf8/src/is_utf8.cpp:3534:37: warning: unused function 'count_ones' [-Wunused-function]
is_utf8_really_inline long long int count_ones(uint64_t input_num) {
                                    ^
../deps/is_utf8/src/is_utf8.cpp:6134:31: warning: unused function 'expand_and_identify' [-Wunused-function]
is_utf8_really_inline __m512i expand_and_identify(__m512i lane0, __m512i lane1,
                              ^
../deps/is_utf8/src/is_utf8.cpp:6151:31: warning: unused function 'expand_utf8_to_utf32' [-Wunused-function]
is_utf8_really_inline __m512i expand_utf8_to_utf32(__m512i input) {

I'll try to silence them tomorrow or in the next few days if someone does not do it before me.