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DEFAULT_CHUNK_THRESHOLD is configurable via Preferences.jl #582

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Aug 8, 2022
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DEFAULT_CHUNK_THRESHOLD is configurable via Preferences.jl #582

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DEFAULT_CHUNK_THRESHOLD is configurable via Preferences.jl
lassepe Apr 23, 2022
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lassepe Aug 7, 2022
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6 changes: 6 additions & 0 deletions docs/src/user/advanced.md
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Expand Up @@ -84,6 +84,12 @@ julia> @time ForwardDiff.gradient!(out, rosenbrock, x, cfg);
0.281853 seconds (4 allocations: 160 bytes)
```

The underlying heuristic will compute a suitable chunk size smaller or equal
to the `ForwardDiff.DEFAULT_CHUNK_THRESHOLD` constant. As of ForwardDiff
v0.10.32 and Julia 1.6, this constant can be configured at load time via
[Preferences.jl](https://github.com/JuliaPackaging/Preferences.jl) by setting the
`default_chunk_threshold` value.

If your input dimension is constant across calls, you should explicitly select a chunk size
rather than relying on ForwardDiff's heuristic. There are two reasons for this. The first is
that ForwardDiff's heuristic depends only on the input dimension, whereas in reality the
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4 changes: 2 additions & 2 deletions src/prelude.jl
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@@ -1,7 +1,9 @@
@static if VERSION >= v"1.6"
const NANSAFE_MODE_ENABLED = @load_preference("nansafe_mode", false)
const DEFAULT_CHUNK_THRESHOLD = @load_preference("default_chunk_threshold", 12)
else
const NANSAFE_MODE_ENABLED = false
const DEFAULT_CHUNK_THRESHOLD = 12
end

const AMBIGUOUS_TYPES = (AbstractFloat, Irrational, Integer, Rational, Real, RoundingMode)
Expand All @@ -10,8 +12,6 @@ const UNARY_PREDICATES = Symbol[:isinf, :isnan, :isfinite, :iseven, :isodd, :isr

const BINARY_PREDICATES = Symbol[:isequal, :isless, :<, :>, :(==), :(!=), :(<=), :(>=)]

const DEFAULT_CHUNK_THRESHOLD = 12

struct Chunk{N} end

const CHUNKS = [Chunk{i}() for i in 1:DEFAULT_CHUNK_THRESHOLD]
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