Enhancing indexOfDiff efficiency in large input slices
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AArch64 Processor rev 0 (aarch64) vendor Kirin820 fn/T/len elapsed
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indexOfDiff_V1/u8/5 19ns
indexOfDiff_V2/u8/5 21ns
std.mem.eql/u8/5 9ns
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indexOfDiff_V1/u8/10 31ns
indexOfDiff_V2/u8/10 16ns
std.mem.eql/u8/10 9ns
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indexOfDiff_V1/u8/20 55ns
indexOfDiff_V2/u8/20 27ns
std.mem.eql/u8/20 13ns
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indexOfDiff_V1/u8/50 129ns
indexOfDiff_V2/u8/50 39ns
std.mem.eql/u8/50 26ns
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indexOfDiff_V1/u8/100 254ns
indexOfDiff_V2/u8/100 52ns
std.mem.eql/u8/100 41ns
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indexOfDiff_V1/u8/1000 2.667us
indexOfDiff_V2/u8/1000 359ns
std.mem.eql/u8/1000 356ns
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indexOfDiff_V1/u8/10000 15.768us
indexOfDiff_V2/u8/10000 3.449us
std.mem.eql/u8/10000 3.591us
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indexOfDiff_V1/u32/5 7ns
indexOfDiff_V2/u32/5 14ns
std.mem.eql/u32/5 7ns
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indexOfDiff_V1/u32/10 14ns
indexOfDiff_V2/u32/10 36ns
std.mem.eql/u32/10 10ns
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indexOfDiff_V1/u32/20 27ns
indexOfDiff_V2/u32/20 20ns
std.mem.eql/u32/20 15ns
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indexOfDiff_V1/u32/50 66ns
indexOfDiff_V2/u32/50 44ns
std.mem.eql/u32/50 38ns
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indexOfDiff_V1/u32/100 132ns
indexOfDiff_V2/u32/100 72ns
std.mem.eql/u32/100 68ns
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indexOfDiff_V1/u32/1000 1.363us
indexOfDiff_V2/u32/1000 1.038us
std.mem.eql/u32/1000 980ns
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indexOfDiff_V1/u32/10000 11.881us
indexOfDiff_V2/u32/10000 5.994us
std.mem.eql/u32/10000 6.089us
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indexOfDiff_V1/u128/5 10ns
indexOfDiff_V2/u128/5 17ns
std.mem.eql/u128/5 12ns
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indexOfDiff_V1/u128/10 18ns
indexOfDiff_V2/u128/10 28ns
std.mem.eql/u128/10 31ns
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indexOfDiff_V1/u128/20 35ns
indexOfDiff_V2/u128/20 50ns
std.mem.eql/u128/20 45ns
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indexOfDiff_V1/u128/50 90ns
indexOfDiff_V2/u128/50 115ns
std.mem.eql/u128/50 113ns
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indexOfDiff_V1/u128/100 204ns
indexOfDiff_V2/u128/100 232ns
std.mem.eql/u128/100 228ns
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indexOfDiff_V1/u128/1000 2.279us
indexOfDiff_V2/u128/1000 2.45us
std.mem.eql/u128/1000 2.323us
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indexOfDiff_V1/u128/10000 26.107us
indexOfDiff_V2/u128/10000 25.562us
std.mem.eql/u128/10000 25.135us |
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Background
The previous
std.mem.indexOfDiffwas implemented with a naive while loop, whose performance relies on the compiler's auto-vectorization. When processing large input data, it fails to fully utilize the CPU's capabilities, resulting in longer execution times. Therefore, I attempted to optimizestd.mem.indexOfDiffby referencingstd.mem.eqlto better leverage CPU performance.The optimization strategy is as follows:
shortest < @sizeOf(usize): Use a while loop.shortest <= @sizeOf(usize) * 2 or vec_len == 0: Use SWAR.shortest < vec_len: Choose a smaller but appropriate vector length.shortest >= vec_len: Use that vector length and perform loop unrolling.Benchmark
indexOfDiff(V1):std.mem.indexOfDiffindexOfDiff(V2): cur impleql:std.mem.eqlcpu: AMD Ryzen 7 3750H with Radeon Vega Mobile Gfx
fn/T/len elapsed --------------------------------------- indexOfDiff_V1/u8/1 1ns indexOfDiff_V2/u8/1 3ns std.mem.eql/u8/1 1ns --------------------------------------- indexOfDiff_V1/u8/5 3ns indexOfDiff_V2/u8/5 3ns std.mem.eql/u8/5 2ns --------------------------------------- indexOfDiff_V1/u8/10 4ns indexOfDiff_V2/u8/10 2ns std.mem.eql/u8/10 2ns --------------------------------------- indexOfDiff_V1/u8/20 9ns indexOfDiff_V2/u8/20 3ns std.mem.eql/u8/20 1ns --------------------------------------- indexOfDiff_V1/u8/50 31ns indexOfDiff_V2/u8/50 6ns std.mem.eql/u8/50 3ns --------------------------------------- indexOfDiff_V1/u8/100 56ns indexOfDiff_V2/u8/100 9ns std.mem.eql/u8/100 5ns --------------------------------------- indexOfDiff_V1/u8/1000 411ns indexOfDiff_V2/u8/1000 117ns std.mem.eql/u8/1000 126ns --------------------------------------- indexOfDiff_V1/u8/10000 3.226us indexOfDiff_V2/u8/10000 820ns std.mem.eql/u8/10000 814ns --------------------------------------- indexOfDiff_V1/u32/1 0ns indexOfDiff_V2/u32/1 1ns std.mem.eql/u32/1 3ns --------------------------------------- indexOfDiff_V1/u32/5 3ns indexOfDiff_V2/u32/5 3ns std.mem.eql/u32/5 2ns --------------------------------------- indexOfDiff_V1/u32/10 4ns indexOfDiff_V2/u32/10 7ns std.mem.eql/u32/10 2ns --------------------------------------- indexOfDiff_V1/u32/20 15ns indexOfDiff_V2/u32/20 9ns std.mem.eql/u32/20 3ns --------------------------------------- indexOfDiff_V1/u32/50 32ns indexOfDiff_V2/u32/50 14ns std.mem.eql/u32/50 15ns --------------------------------------- indexOfDiff_V1/u32/100 56ns indexOfDiff_V2/u32/100 38ns std.mem.eql/u32/100 37ns --------------------------------------- indexOfDiff_V1/u32/1000 546ns indexOfDiff_V2/u32/1000 349ns std.mem.eql/u32/1000 385ns --------------------------------------- indexOfDiff_V1/u32/10000 4.555us indexOfDiff_V2/u32/10000 3.363us std.mem.eql/u32/10000 3.42us --------------------------------------- indexOfDiff_V1/u128/1 0ns indexOfDiff_V2/u128/1 0ns std.mem.eql/u128/1 3ns --------------------------------------- indexOfDiff_V1/u128/5 6ns indexOfDiff_V2/u128/5 9ns std.mem.eql/u128/5 4ns --------------------------------------- indexOfDiff_V1/u128/10 15ns indexOfDiff_V2/u128/10 17ns std.mem.eql/u128/10 8ns --------------------------------------- indexOfDiff_V1/u128/20 29ns indexOfDiff_V2/u128/20 27ns std.mem.eql/u128/20 26ns --------------------------------------- indexOfDiff_V1/u128/50 84ns indexOfDiff_V2/u128/50 60ns std.mem.eql/u128/50 62ns --------------------------------------- indexOfDiff_V1/u128/100 154ns indexOfDiff_V2/u128/100 149ns std.mem.eql/u128/100 169ns --------------------------------------- indexOfDiff_V1/u128/1000 1.567us indexOfDiff_V2/u128/1000 1.595us std.mem.eql/u128/1000 1.772us --------------------------------------- indexOfDiff_V1/u128/10000 15.069us indexOfDiff_V2/u128/10000 14.597us std.mem.eql/u128/10000 13.783us