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Date: Thu, 25 Jan 2024 06:21:25 +0100
Message-ID: <CAJmy8YE5Q81jv4rENfNmLifNVL5erCF2rknGKGSaa2Eo1ww2eg@mail.gmail.com>
To: Marco Pivetta <ocramius@gmail.com>
Cc: tag Knife <fenniclog@gmail.com>, Hans Henrik Bergan <hans@loltek.net>, internals@lists.php.net
Content-Type: text/plain; charset="UTF-8"
Subject: Re: [PHP-DEV] BLAKE3 hash
From: divinity76@gmail.com (Hans Henrik Bergan)

On Wed, 24 Jan 2024 at 17:59, Marco Pivetta <ocramius@gmail.com> wrote:
>
> Depends on the actual numbers: is there any way to make a comparison that
> is relatively stable across architectures?
>
> Would it be feasible to start with the
> cross-platform-let-the-compiler-do-its-job version (that somebody may
> actually be capable of auditing), and then introduce other versions when
> the jump is significant enough?
>

don't know about "relatively stable across architectures" but wrote
some benchmarking code, keep reading.



On Wed, 24 Jan 2024 at 17:55, tag Knife <fenniclog@gmail.com> wrote:
> Should we even be considering the specific instruction implementations?
> I've always been in the camp
> of you are not smarter than the compiler. As even the best human written
> ASM code can be slower
> than the obscure instructions the compiler might choose to use in a weird
> and wonderful way.

The BLAKE3 team is smarter than GCC11.4, even with -march=native
-mtune=native, which is *not* commonly used in PHP,
the compiler didn't stand a chance against the hand-optimized assembly versions,

wrote some benchmarks, but the TL;DR is:
portable -O2 usually used by PHP managed 1126MB/s,
portable -O2 -march=native managed 533MB/s (wtf? gcc obviously got
something wrong here),
hand-written -O2 SSE2  managed 3144MB/s,
hand-written -O2 SSE41 managed 3332MB/s,
hand-written -O2 avx2 managed 6554MB/s,
hand-writen -O2 AVX512 managed 8913MB/s,
on my AMD Ryzen 9 7950x,
benchmarking code:
https://gist.github.com/divinity76/5729472dd5d77e94cd0acb245aac2226
raw output:
array(6) {
  ["O2-portable-march"]=>
  array(2) {
    ["microseconds_for_16_kib"]=>
    int(29295)
    ["mb_per_second"]=>
    float(533.3674688513398)
  }
  ["O2-portable"]=>
  array(2) {
    ["microseconds_for_16_kib"]=>
    int(13876)
    ["mb_per_second"]=>
    float(1126.0449697319111)
  }
  ["O2-sse2"]=>
  array(2) {
    ["microseconds_for_16_kib"]=>
    int(4969)
    ["mb_per_second"]=>
    float(3144.4958744214127)
  }
  ["O2-sse41"]=>
  array(2) {
    ["microseconds_for_16_kib"]=>
    int(4688)
    ["mb_per_second"]=>
    float(3332.977815699659)
  }
  ["O2-avx2"]=>
  array(2) {
    ["microseconds_for_16_kib"]=>
    int(2384)
    ["mb_per_second"]=>
    float(6554.1107382550335)
  }
  ["O2-avx512"]=>
  array(2) {
    ["microseconds_for_16_kib"]=>
    int(1753)
    ["mb_per_second"]=>
    float(8913.291500285226)
  }
}