Added new ScanPrefix accumulate algorithm
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…ed prefixes (one extra kernel launch), with that `ScanPrefixes` algorithm becoming the default on Metal.
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We're still faster than the current default Metal accumulate: using BenchmarkTools
using Metal
import AcceleratedKernels as AK
using Random
Random.seed!(0)
function akacc(v)
va = AK.accumulate(+, v, init=zero(eltype(v)), block_size=1024)
Metal.synchronize()
va
end
function baseacc(v)
va = accumulate(+, v, init=zero(eltype(v)))
Metal.synchronize()
va
end
v = MtlArray(rand(1:100, 10_000_000))
# Correctness checks
va = akacc(v) |> Array
vb = baseacc(v) |> Array
@assert va == vb
# Benchmarks
println("Base vs AK")
display(@benchmark baseacc($v))
display(@benchmark akacc($v))And timings: julia> include("accumulate_benchmark.jl")
Base vs AK
BenchmarkTools.Trial: 603 samples with 1 evaluation.
Range (min … max): 3.369 ms … 52.091 ms ┊ GC (min … max): 0.00% … 0.00%
Time (median): 7.746 ms ┊ GC (median): 0.00%
Time (mean ± σ): 8.300 ms ± 6.782 ms ┊ GC (mean ± σ): 0.00% ± 0.00%
█▆▄▁ ▁ ▅▇▅▂
█████████████▇▅▇▇▆▇▅▆▅▄▅▄▄▁▄▁▁▅▁▅▁▆▆▄▆▄▇▅▄▄▄▄▁▁▁▁▁▁▁▁▁▄▄▅▆ ▇
3.37 ms Histogram: log(frequency) by time 36.9 ms <
Memory estimate: 45.41 KiB, allocs estimate: 1568.
BenchmarkTools.Trial: 644 samples with 1 evaluation.
Range (min … max): 4.535 ms … 35.595 ms ┊ GC (min … max): 0.00% … 0.00%
Time (median): 5.928 ms ┊ GC (median): 0.00%
Time (mean ± σ): 7.770 ms ± 4.089 ms ┊ GC (mean ± σ): 0.00% ± 0.00%
█▅▁ ▁▂▁▂▄▄▃▂
███▇▆▁▆██████████▇▄▆▆▇▆▇▅▇▅▆▁▁▅▁▁▁▄▄▁▁▄▁▁▄▄▁▁▁▅▁▁▁▁▁▁▄▄▁▁▄ ▇
4.53 ms Histogram: log(frequency) by time 27.6 ms <
Memory estimate: 16.63 KiB, allocs estimate: 565. |
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Added second accumulate algorithm using coupled lookback of pre-scanned prefixes (=> one extra kernel launch), with that
ScanPrefixesalgorithm becoming the default on Metal.This fixes the decoupled-lookback issue on Metal.