[ARM64] Performance regression: Utf8Encoding

[adamsitnik]

After running benchmarks for 3.1 vs 5.0 using "Ubuntu arm64 Qualcomm Machines" owned by the JIT Team, I've found few regressions related to Utf8Encoding. They are alll reproducible and I've verified that it's not a matter of loop alignment (by running them with --envVars COMPlus_JitAlignLoops:1).

It looks like it's ARM64 specific regression, I was not able to reproduce it for ARM (the 32 bit variant).

Repro

git clone https://github.com/dotnet/performance.git
python3 ./performance/scripts/benchmarks_ci.py -f netcoreapp3.1 netcoreapp5.0 --architecture arm64 --filter Perf_Utf8Encoding

BenchmarkDotNet=v0.12.1.1405-nightly, OS=ubuntu 16.04
Unknown processor
[Host] : .NET Core 3.1.8 (CoreCLR 4.700.20.41105, CoreFX 4.700.20.41903), Arm64 RyuJIT
Job-VTSQOV : .NET Core 3.1.8 (CoreCLR 4.700.20.41105, CoreFX 4.700.20.41903), Arm64 RyuJIT
Job-RAMSQZ : .NET Core 5.0.0 (CoreCLR 5.0.20.41714, CoreFX 5.0.20.41714), Arm64 RyuJIT

Method	Runtime	Input	Mean	Ratio	Allocated
GetByteCount	.NET Core 3.1	EnglishAllAscii	38.00 us	1.00	-
GetByteCount	.NET Core 5.0	EnglishAllAscii	40.66 us	1.07	-
GetBytes	.NET Core 3.1	EnglishAllAscii	101.09 us	1.00	163840 B
GetBytes	.NET Core 5.0	EnglishAllAscii	104.96 us	1.04	163855 B
GetString	.NET Core 3.1	EnglishAllAscii	103.47 us	1.00	327648 B
GetString	.NET Core 5.0	EnglishAllAscii	95.76 us	0.93	327677 B
GetByteCount	.NET Core 3.1	EnglishMostlyAscii	117.50 us	1.00	-
GetByteCount	.NET Core 5.0	EnglishMostlyAscii	221.40 us	1.88	-
GetBytes	.NET Core 3.1	EnglishMostlyAscii	273.49 us	1.00	169880 B
GetBytes	.NET Core 5.0	EnglishMostlyAscii	377.67 us	1.38	169895 B
GetString	.NET Core 3.1	EnglishMostlyAscii	262.55 us	1.00	327656 B
GetString	.NET Core 5.0	EnglishMostlyAscii	250.18 us	0.95	327685 B
GetByteCount	.NET Core 3.1	Chinese	53.34 us	1.00	-
GetByteCount	.NET Core 5.0	Chinese	90.21 us	1.69	-
GetBytes	.NET Core 3.1	Chinese	245.94 us	1.00	177752 B
GetBytes	.NET Core 5.0	Chinese	279.62 us	1.14	177768 B
GetString	.NET Core 3.1	Chinese	373.80 us	1.00	150112 B
GetString	.NET Core 5.0	Chinese	358.11 us	0.96	150126 B
GetByteCount	.NET Core 3.1	Cyrillic	45.35 us	1.00	-
GetByteCount	.NET Core 5.0	Cyrillic	76.01 us	1.68	-
GetBytes	.NET Core 3.1	Cyrillic	193.34 us	1.00	100880 B
GetBytes	.NET Core 5.0	Cyrillic	222.10 us	1.15	100889 B
GetString	.NET Core 3.1	Cyrillic	262.69 us	1.00	130856 B
GetString	.NET Core 5.0	Cyrillic	259.83 us	0.99	130868 B
GetByteCount	.NET Core 3.1	Greek	58.36 us	1.00	-
GetByteCount	.NET Core 5.0	Greek	97.41 us	1.67	-
GetBytes	.NET Core 3.1	Greek	275.88 us	1.00	129248 B
GetBytes	.NET Core 5.0	Greek	314.00 us	1.14	129260 B
GetString	.NET Core 3.1	Greek	394.55 us	1.00	164264 B
GetString	.NET Core 5.0	Greek	394.35 us	1.00	164278 B

Docs

Profiling workflow for dotnet/runtime repository
Benchmarking workflow for dotnet/runtime repository

cc @kunalspathak @carlossanlop @pgovind @tannergooding

Tagging subscribers to this area: @tarekgh, @krwq
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[tarekgh]

I have changed the tag to jit for now as this is most likely not the UTF8Encoding code itself. if proven otherwise, please re-tag it with encoding label again.

[kunalspathak]

@jeffhandley , @BruceForstall , @JulieLeeMSFT

[pgovind]

Just adding a note here: Despite what the name suggests, the 4 regressions listed here are likely from methods in UTF8Utility and/or ASCIIUtility. The GetString benchmark doesn't seem to show any improvements, but it's not straightforward to reverse the changes that this benchmark hits because the UTF8Utility and ASCIIUtility methods are highly coupled and they do show decent speedup in the other benchmarks.

[JulieLeeMSFT]

@echesakovMSFT please look into this.

CC @AndyAyersMS