arm: optimize decoder on Arm SVE2 platform

[cyb70289]

This patch improves sonic json decoder performance on Arm SVE2 CPU. It leverages SVMATCH instruction to locate multiple tokens in a vector efficiently.

Enable this feature by specifying cmake option "-DENABLE_SVE2_128=ON". Please note the binary can only run on hardware with SVE2 supported, and the vector size must be 128 bits, like Neoverse-N2. Otherwise, the code behaviour is undefined.

As shown in the table below, tested on Bluewhale server, obvious performance uplift is observed from sonic decoder benchmarks. No side effect observed for other benchmarks.

Benchmark	Original	SVE2	Improvement
gsoc-2018/Decode_SonicDyn	2.38736	2.76677	15.89%
citm_catalog/Decode_SonicDyn	1.41729	1.76191	24.32%
otfcc/Decode_SonicDyn	399.916	413.417	3.38%
fgo/Decode_SonicDyn	691.597	716.301	3.57%
twitter/Decode_SonicDyn	1.33604	1.58737	18.81%
twitterescaped/Decode_SonicDyn	1.24759	1.30216	4.37%
github_events/Decode_SonicDyn	1.38961	1.65635	19.20%
canada/Decode_SonicDyn	526.145	524.517	-0.31%
poet/Decode_SonicDyn	2.06297	2.40383	16.52%
lottie/Decode_SonicDyn	419.902	438.824	4.51%
book/Decode_SonicDyn	456.615	487.196	6.70%

[xiegx94]

@cyb70289 What's unit of your benchmark results? HIB or LIB?

[cyb70289]

@cyb70289 What's unit of your benchmark results? HIB or LIB?

Gi/s and Mi/s, bytes per second.

As an example

$ build/benchmark/bench --benchmark_filter=Decode_Sonic
gsoc-2018/Decode_SonicDyn         1299148 ns      1299146 ns          537 bytes_per_second=2.38563Gi/s testdata/gsoc-2018.json
citm_catalog/Decode_SonicDyn      1136378 ns      1136290 ns          617 bytes_per_second=1.41565Gi/s testdata/citm_catalog.json
otfcc/Decode_SonicDyn           158508828 ns    158472460 ns            4 bytes_per_second=399.646Mi/s testdata/otfcc.json
fgo/Decode_SonicDyn              67084470 ns     67084360 ns            9 bytes_per_second=692.246Mi/s testdata/fgo.json
......

[xiegx94]

see #56，support sve as a different arch.

[cyb70289]

Thanks, will try to refactor following that PR. Instead of adding a complete SVE implementation, I'm thinking about "inherit" from NEON and only override code that can benefit from SVE. Looks to me many code will be the same for NEON and SVE.

[cyb70289]

@xiegx94 , sve2-128 implementation is added. Arm common code is moved to common/arm_common/. I checked sonic decoder benchmarks, no performance regression is found.

[cyb70289]

Any convenient way to run clang-format job locally?

[xiegx94]

Any convenient way to run clang-format job locally?

Could you install clang in your machine? If you have a clang-format, run git clang-format

[cyb70289]

Any convenient way to run clang-format job locally?

Could you install clang in your machine? If you have a clang-format, run git clang-format

Thanks, format should be fixed now.

[cyb70289]

"Test coverage" runs successfully on my local x86 server. Not sure why CI job fails. Looks it's only for x86?

[xiegx94]

@cyb70289 pls update cmake/set_arch_flags.cmake.

[xiegx94]

93 FYI @cyb70289

[cyb70289]

@cyb70289 pls update cmake/set_arch_flags.cmake.

@xiegx94 updated