[webkit-dev] Proposal: Using LLInt Asm in major architectures even if JIT is disabled

[Yusuke Suzuki]

Hi WebKittens!

Recently, node-jsc is announced[1]. When I read the documents of that
project,
I found that they use LLInt ASM interpreter instead of CLoop in non-JIT
environment.
So I had one question in my mind: How fast the LLInt ASM interpreter when
comparing to CLoop?

I've set up two builds. One is CLoop build (-DENABLE_JIT=OFF) and another
is JIT build JSC with `JSC_useJIT=false`.
And I've ran kraken benchmarks with these two builds in x64 Linux machine.
The results are the followings.

Benchmark report for Kraken on sakura-trick.

VMs tested:
"baseline" at
/home/yusukesuzuki/dev/WebKit/WebKitBuild/nojit/Release/bin/jsc
"patched" at
/home/yusukesuzuki/dev/WebKit/WebKitBuild/nojit-llint/Release/bin/jsc

Collected 10 samples per benchmark/VM, with 10 VM invocations per
benchmark. Emitted a call to gc() between sample
measurements. Used 1 benchmark iteration per VM invocation for warm-up.
Used the jsc-specific preciseTime()
function to get microsecond-level timing. Reporting benchmark execution
times with 95% confidence intervals in
milliseconds.

                                           baseline
patched

ai-astar                              3619.974+-57.095     ^
2014.835+-59.016        ^ definitely 1.7967x faster
audio-beat-detection                  1762.085+-24.853     ^
1030.902+-19.743        ^ definitely 1.7093x faster
audio-dft                             1822.426+-28.704     ^
909.262+-16.640        ^ definitely 2.0043x faster
audio-fft                             1651.070+-9.994      ^
865.203+-7.912         ^ definitely 1.9083x faster
audio-oscillator                      1853.697+-26.539     ^
992.406+-12.811        ^ definitely 1.8679x faster
imaging-darkroom                      2118.737+-23.219     ^
1303.729+-8.071         ^ definitely 1.6251x faster
imaging-desaturate                    3133.654+-28.545     ^
1759.738+-18.182        ^ definitely 1.7808x faster
imaging-gaussian-blur                16321.090+-154.893    ^
7228.017+-58.508        ^ definitely 2.2580x faster
json-parse-financial                    57.256+-2.876
56.101+-4.265           might be 1.0206x faster
json-stringify-tinderbox                38.470+-2.788      ?
38.771+-0.935         ?
stanford-crypto-aes                    851.341+-7.738      ^
485.438+-13.904        ^ definitely 1.7538x faster
stanford-crypto-ccm                    556.133+-6.606      ^
264.161+-3.970         ^ definitely 2.1053x faster
stanford-crypto-pbkdf2                1945.718+-15.968     ^
1075.013+-13.337        ^ definitely 1.8099x faster
stanford-crypto-sha256-iterative       623.203+-7.604      ^
349.782+-12.810        ^ definitely 1.7817x faster

<arithmetic>                          2596.775+-14.857     ^
1312.383+-8.840         ^ definitely 1.9787x faster

Surprisingly, LLInt ASM interpreter is significantly faster than CLoop. I
expected it would be fast, but it would show around 10% performance win.
But the reality is that it is 2x faster. It is too much number to me to
consider enabling LLInt ASM interpreter for non-JIT build configuration.
As a bonus, LLInt ASM interpreter offers sampling profiler support even in
non-JIT environment.

So my proposal is, how about enabling LLInt ASM interpreter in non-JIT
configuration environment in major architectures (x64 and ARM64)?

Best regards,
Yusuke Suzuki

[1]:
https://lists.webkit.org/pipermail/webkit-dev/2018-September/030140.html
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