mirror of
https://github.com/codedownio/time-ghc-modules.git
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88 lines
2.5 KiB
Markdown
88 lines
2.5 KiB
Markdown
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# time-ghc-modules
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Figure out why your builds are slow. This tool analyzes how long it takes GHC to compile your Haskell modules, broken down by phase.
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# Quick start
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``` shell
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cd <my-project>
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stack clean
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stack build --ghc-options "-ddump-to-file -ddump-timings"
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# ----- OR -----
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cabal clean
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cabal build all --ghc-options "-ddump-to-file -ddump-timings"
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```
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If you have Nix, you can simply run `time-ghc-modules` from Nixpkgs!
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``` shell
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nix run nixpkgs#time-ghc-modules
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```
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Or, clone the repo first:
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``` shell
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git clone git@github.com:codedownio/time-ghc-modules.git /path/to/time-ghc-modules
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# If you have Nix, you can use the fully reproducible version
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/path/to/time-ghc-modules/time-ghc-modules-nix
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# Otherwise, your system needs to have SQLite >= 3.33.0, Python 3, and sed
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/path/to/time-ghc-modules/time-ghc-modules
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```
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The script will search for all your `*.dump-timings` files and analyze them. It will finish by printing out the path to an HTML file:
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``` shell
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...
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--> Wrote report at file:///tmp/tmp.pvnp4FYmLa/report.html
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```
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# Example: hledger
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You can generate the time report below for [hledger](https://github.com/simonmichael/hledger) by running the following commands (assuming you have Nix).
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``` shell
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set -e
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cd $(mktemp -d)
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git clone git@github.com:simonmichael/hledger.git
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git clone git@github.com:codedownio/time-ghc-modules.git
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cd hledger
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stack build --ghc-options "-ddump-to-file -ddump-timings"
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../time-ghc-modules/time-ghc-modules-nix
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```
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# Tips
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* The script will output its log messages to `stderr` and print the final report path to `stdout` (assuming it didn't exit with a failure). This makes it easy to use the output in scripts. For example:
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``` shell
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# Build the report and open it in your browser
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> firefox $(/path/to/time-ghc-modules/time-ghc-modules)
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```
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``` shell
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# Build the report in CI and stash it somewhere
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> cp $(/path/to/time-ghc-modules/time-ghc-modules) $MY_CI_ARTIFACTS_DIR/
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```
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* You can also look at the timing of individual components, but doing e.g. `stack build some-component:lib`. But, make sure to clean up any old `.dump-timings` files from previous runs:
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``` shell
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find . -name "*.dump-timings" | xargs rm
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```
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* GHC's `-dumpdir` option can be used to consolidate the `.dump-timings` files, so they aren't left all over your source tree. For example:
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``` shell
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stack build --ghc-options "-ddump-to-file -ddump-timings -dumpdir .ghcdump"
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```
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# Compatibility
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The flag `-ddump-timings` is available for `GHC >= 8.4.1`.
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