# Build profiling instructions There are three ways you can get information about compile times: 1. Just using `time ninja install` instead of `ninja install` to time it overall. 2. Reading ninja's log files to get a per-file compile time. 3. Enabling GCC or Clang flags to get a more detailed per-file breakdown of times for compiler passes within a file. ## Ninja log files Ninja produces a handy log file that includes a per-cpp-file compilation time. This is useful for discovering which files take the most time, and so are good targets for speeding up the overall build time. A python3 script named `ninjatracing` converts the ninja log file into a JSON format that's readable by several profile viewers. ### Prerequisites `ninjatracing` is available on [GitHub](https://github.com/nico/ninjatracing/blob/master/ninjatracing) It requires `python3`, available at `python`. You can either create the symlink yourself, or just modify the ninjatracing file to say `python3` instead of `python`. You also need to make sure `ninjatracing` is marked as executable, and available from your PATH (or somewhere convenient where you can manually call it from). ### Usage First, we need to clean the build (and `ccache` if present) to make sure every file gets compiled and gives a meaningful time reading. ```console ninja clean ccache --clear ``` Then, execute ninja as normal: ```console ninja ``` The log will be written to `.ninja_log` in the current directory by default. To convert it to the more useful JSON file, call `ninjatracing` from the directory you called ninja from: ```console ninjatracing .ninja_log > trace.json ``` You can then drag-and-drop the file onto [Speedscope](https://www.speedscope.app/) or any other compatible flamegraph visualizer. ## GCC/Clang Adding the `-ftime-report` flag to GCC will cause it to output a breakdown for each file it compiles, which looks like this:
GCC -ftime-report output ```console Time variable usr sys wall GGC phase setup : 0.00 ( 0%) 0.00 ( 0%) 0.01 ( 0%) 1326k ( 2%) phase parsing : 0.57 ( 61%) 0.19 ( 83%) 1.63 ( 65%) 59M ( 74%) phase lang. deferred : 0.10 ( 11%) 0.03 ( 13%) 0.30 ( 12%) 8761k ( 11%) phase opt and generate : 0.23 ( 25%) 0.01 ( 4%) 0.48 ( 19%) 10M ( 13%) phase last asm : 0.03 ( 3%) 0.00 ( 0%) 0.08 ( 3%) 539k ( 1%) |name lookup : 0.11 ( 12%) 0.01 ( 4%) 0.25 ( 10%) 2004k ( 2%) |overload resolution : 0.08 ( 9%) 0.00 ( 0%) 0.26 ( 10%) 7900k ( 10%) dump files : 0.02 ( 2%) 0.00 ( 0%) 0.00 ( 0%) 0 ( 0%) callgraph construction : 0.04 ( 4%) 0.00 ( 0%) 0.06 ( 2%) 2677k ( 3%) callgraph optimization : 0.00 ( 0%) 0.00 ( 0%) 0.01 ( 0%) 4752 ( 0%) callgraph functions expansion : 0.15 ( 16%) 0.00 ( 0%) 0.32 ( 13%) 6267k ( 8%) callgraph ipa passes : 0.03 ( 3%) 0.01 ( 4%) 0.08 ( 3%) 1413k ( 2%) ipa inheritance graph : 0.00 ( 0%) 0.00 ( 0%) 0.02 ( 1%) 3760 ( 0%) ipa profile : 0.00 ( 0%) 0.00 ( 0%) 0.01 ( 0%) 0 ( 0%) trivially dead code : 0.01 ( 1%) 0.00 ( 0%) 0.00 ( 0%) 224 ( 0%) df reg dead/unused notes : 0.01 ( 1%) 0.00 ( 0%) 0.00 ( 0%) 104k ( 0%) alias analysis : 0.01 ( 1%) 0.00 ( 0%) 0.00 ( 0%) 70k ( 0%) preprocessing : 0.06 ( 6%) 0.03 ( 13%) 0.16 ( 6%) 1365k ( 2%) parser (global) : 0.04 ( 4%) 0.04 ( 17%) 0.13 ( 5%) 6894k ( 8%) parser struct body : 0.09 ( 10%) 0.03 ( 13%) 0.20 ( 8%) 9020k ( 11%) parser function body : 0.00 ( 0%) 0.00 ( 0%) 0.01 ( 0%) 83k ( 0%) parser inl. func. body : 0.03 ( 3%) 0.01 ( 4%) 0.05 ( 2%) 1567k ( 2%) parser inl. meth. body : 0.11 ( 12%) 0.03 ( 13%) 0.30 ( 12%) 10M ( 13%) template instantiation : 0.27 ( 29%) 0.08 ( 35%) 0.89 ( 36%) 25M ( 32%) constant expression evaluation : 0.01 ( 1%) 0.00 ( 0%) 0.01 ( 0%) 356k ( 0%) constraint satisfaction : 0.01 ( 1%) 0.00 ( 0%) 0.02 ( 1%) 130k ( 0%) early inlining heuristics : 0.00 ( 0%) 0.00 ( 0%) 0.02 ( 1%) 21k ( 0%) inline parameters : 0.01 ( 1%) 0.00 ( 0%) 0.03 ( 1%) 146k ( 0%) integration : 0.00 ( 0%) 0.00 ( 0%) 0.01 ( 0%) 564k ( 1%) tree CFG cleanup : 0.00 ( 0%) 0.00 ( 0%) 0.01 ( 0%) 5768 ( 0%) tree SSA other : 0.00 ( 0%) 0.00 ( 0%) 0.01 ( 0%) 13k ( 0%) tree operand scan : 0.01 ( 1%) 0.00 ( 0%) 0.00 ( 0%) 429k ( 1%) tree CCP : 0.01 ( 1%) 0.00 ( 0%) 0.00 ( 0%) 18k ( 0%) expand : 0.01 ( 1%) 0.00 ( 0%) 0.03 ( 1%) 1303k ( 2%) varconst : 0.00 ( 0%) 0.00 ( 0%) 0.04 ( 2%) 6744 ( 0%) forward prop : 0.01 ( 1%) 0.00 ( 0%) 0.02 ( 1%) 3520 ( 0%) CSE : 0.01 ( 1%) 0.00 ( 0%) 0.00 ( 0%) 1144 ( 0%) loop fini : 0.00 ( 0%) 0.00 ( 0%) 0.01 ( 0%) 0 ( 0%) branch prediction : 0.00 ( 0%) 0.01 ( 4%) 0.00 ( 0%) 20k ( 0%) combiner : 0.01 ( 1%) 0.00 ( 0%) 0.02 ( 1%) 138k ( 0%) integrated RA : 0.01 ( 1%) 0.00 ( 0%) 0.01 ( 0%) 1112k ( 1%) LRA reload inheritance : 0.00 ( 0%) 0.00 ( 0%) 0.02 ( 1%) 13k ( 0%) LRA create live ranges : 0.00 ( 0%) 0.00 ( 0%) 0.01 ( 0%) 8568 ( 0%) reload CSE regs : 0.01 ( 1%) 0.00 ( 0%) 0.02 ( 1%) 100k ( 0%) final : 0.00 ( 0%) 0.00 ( 0%) 0.02 ( 1%) 323k ( 0%) variable output : 0.01 ( 1%) 0.00 ( 0%) 0.00 ( 0%) 15k ( 0%) symout : 0.09 ( 10%) 0.00 ( 0%) 0.20 ( 8%) 13M ( 17%) variable tracking : 0.00 ( 0%) 0.00 ( 0%) 0.04 ( 2%) 471k ( 1%) var-tracking dataflow : 0.02 ( 2%) 0.00 ( 0%) 0.03 ( 1%) 18k ( 0%) var-tracking emit : 0.00 ( 0%) 0.00 ( 0%) 0.04 ( 2%) 117k ( 0%) rest of compilation : 0.01 ( 1%) 0.00 ( 0%) 0.03 ( 1%) 1258k ( 2%) TOTAL : 0.93 0.23 2.50 79M [24/3139] Building CXX object Kernel/CMakeFiles/Kernel.dir/CommandLine.cpp.o ```
Depending on whether you understand the internals of the compiler, this may or may not be helpful to you! Generally, this is not recommended. Clang also supports `-ftime-report`, but I have not tested the output for it. To add the flag, edit the `CMakeLists.txt` in the ladybird root directory, and add `add_compile_options(-ftime-report)` to the list of compile options that start around line 220. Additionally, you can add `-ftime-report-details` too, which again I have not tested.