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Currently, the parser relies on the global experimental feature flags.
In order to properly test conditional language features, we instead need
to pass it around in the parser::State.
This means that the parser cannot cache the result of isEnabled anymore,
which wouldn't necessarily hurt performance if the function didn't
perform a linear search on the list of enabled features on every single
call. While we could simply evaluate once at the start of parsing and
cache the result in the parser state, the more sustainable solution
would be to fix `isEnabled` such that all callers may profit from the
performance improvement.
Change-Id: Ic9b9c5d882b6270e1114988b63e6064d36c25cf2
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Change-Id: I12088e0b618407e5432523bbc97be63c8d6fce62
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this gives about 20% performance improvements on pure parsing. obviously
it will be less on full eval, but depending on how much parsing is to be
done (e.g. including hackage-packages.nix or not) it's more like 4%-10%.
this has been tested (with thousands of core hours of fuzzing) to ensure
that the ASTs produced by the new parser are exactly the same as the old
one would have produced. error messages will change (sometimes by a lot)
and are not yet perfect, but we would rather leave this as is for later.
test results for running only the parser (excluding the variable binding
code) in a tight loop with inputs and parameters as given are promising:
- 40% faster on lix's package.nix at 10000 iterations
- 1.3% faster on nixpkgs all-packages.nix at 1000 iterations
- equivalent on all of nixpkgs concatenated at 100 iterations
(excluding invalid files, each file surrounded with parens)
more realistic benchmarks are somewhere in between the extremes, parsing
once again getting the largest uplift. other realistic workloads improve
by a few percentage points as well, notably system builds are 4% faster.
Benchmarks summary (from ./bench/summarize.jq bench/bench-*.json)
old/bin/nix --extra-experimental-features 'nix-command flakes' eval -f bench/nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix
mean: 0.408s ± 0.025s
user: 0.355s | system: 0.033s
median: 0.389s
range: 0.388s ... 0.442s
relative: 1
new/bin/nix --extra-experimental-features 'nix-command flakes' eval -f bench/nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix
mean: 0.332s ± 0.024s
user: 0.279s | system: 0.033s
median: 0.314s
range: 0.313s ... 0.361s
relative: 0.814
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old/bin/nix --extra-experimental-features 'nix-command flakes' eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
mean: 6.133s ± 0.022s
user: 5.395s | system: 0.437s
median: 6.128s
range: 6.099s ... 6.183s
relative: 1
new/bin/nix --extra-experimental-features 'nix-command flakes' eval --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
mean: 5.925s ± 0.025s
user: 5.176s | system: 0.456s
median: 5.934s
range: 5.861s ... 5.943s
relative: 0.966
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GC_INITIAL_HEAP_SIZE=10g old/bin/nix eval --extra-experimental-features 'nix-command flakes' --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
mean: 4.503s ± 0.027s
user: 3.731s | system: 0.547s
median: 4.499s
range: 4.478s ... 4.541s
relative: 1
GC_INITIAL_HEAP_SIZE=10g new/bin/nix eval --extra-experimental-features 'nix-command flakes' --raw --impure --expr 'with import <nixpkgs/nixos> {}; system'
mean: 4.285s ± 0.031s
user: 3.504s | system: 0.571s
median: 4.281s
range: 4.221s ... 4.328s
relative: 0.951
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old/bin/nix --extra-experimental-features 'nix-command flakes' search --no-eval-cache github:nixos/nixpkgs/e1fa12d4f6c6fe19ccb59cac54b5b3f25e160870 hello
mean: 16.475s ± 0.07s
user: 14.088s | system: 1.572s
median: 16.495s
range: 16.351s ... 16.536s
relative: 1
new/bin/nix --extra-experimental-features 'nix-command flakes' search --no-eval-cache github:nixos/nixpkgs/e1fa12d4f6c6fe19ccb59cac54b5b3f25e160870 hello
mean: 15.973s ± 0.013s
user: 13.558s | system: 1.615s
median: 15.973s
range: 15.946s ... 15.99s
relative: 0.97
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Change-Id: Ie66ec2d045dec964632c6541e25f8f0797319ee2
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