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quarto-dev
GitHub Repository: quarto-dev/quarto-cli
 Path: blob/main/dev-docs/performance-monitoring/pandoc-profiling.md
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To perform fine-grained profiling of Pandoc Lua filters, we use custom binaries:

  • a patch of Lua that supports sample-based profiling

  • a custom binary of Pandoc linked against that version of Lua

Compile the custom Lua version

This has currently only been tested on Macos and Linux.

$ git clone git@github.com:cscheid/lua-fast-profiler.git
$ cd lua-fast-profiler
$ git checkout feature/fast-profiler-5.4
$ make

You should have lua and liblua.a in the lua-fast-profiler directory.

This version of Lua adds a new debugging hook, "time". This hook triggers at specified intervals, and is enabled using the letter t in the debug.sethook call. The debug hook callback also supports the "alarm" hook, used when calling the sethook callback.

Quarto ships with a custom Lua profiler that supports these hooks and performs low-overhead stack profiling.

Compile the custom Pandoc binary

Clone the Pandoc repository, and then

$ C_INCLUDE_PATH=<path-lua-fast-profiler> LIBRARY_PATH=<path-lua-fast-profiler> cabal build pandoc-cli --constraint 'lua +system-lua'

Run Quarto with profiling

To get Lua profiling output from Quarto, use the lua-profiler-output metadata option to provide an output file name, and ensure that Quarto uses the pandoc binary you just compiled.

$ QUARTO_PANDOC=<path-to-built-pandoc> quarto render ...

The output will be written as JSON, in a format compatible with Perfetto. The default sampling interval is 5ms, but you can customize that by setting the lua-profiler-interval-ms metadata option.

Analyze profile

The resulting profile can be visualized and analyzed as a trace file at https://ui.perfetto.dev.

Profiling multiple-file projects

In multiple-file projects, you can get a summary of the runtime of individual filter steps by providing the QUARTO_COMBINED_LUA_PROFILE environment variable. At the end of rendering a project, the name of the file pointed to QUARTO_COMBINED_LUA_PROFILE will contain a CSV file with the columns filter, filename, and time, corresponding to an estimate of time (in microseconds) taken by each stage of Quarto's filtering pipeline.