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SerenityOS provides multiple profiling approaches for analyzing both build performance and runtime behavior.

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Build Profiling

There are three ways to get information about compile times:
  1. Using time ninja install for overall timing
  2. Reading Ninja’s log files for per-file compile times
  3. Enabling GCC/Clang flags for detailed compiler pass breakdowns

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Ninja Log Analysis

Ninja produces a log file with per-cpp-file compilation times, useful for identifying slow-to-compile files.

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Prerequisites

  • ninjatracing - Python script to convert Ninja logs
  • python3 (the script expects python to be available)
  • Make ninjatracing executable and available in your PATH

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Usage

Step 1: Clean the buildClean build artifacts and ccache to ensure every file is compiled:
ninja clean
ccache --clear
Step 2: Build with Ninja
ninja
Step 3: Convert log to JSONThe log is written to .ninja_log in the current directory:
ninjatracing .ninja_log > trace.json
Step 4: VisualizeDrag and drop trace.json onto Speedscope or any compatible flamegraph visualizer.
Ninja trace analysis helps identify which files take the most time, making them good targets for optimization.

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Compiler Time Reports

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GCC -ftime-report

Adding the -ftime-report flag to GCC outputs a breakdown for each compiled file.
Edit CMakeLists.txt in the Serenity root directory and add around line 220:
add_compile_options(-ftime-report)
Optionally add -ftime-report-details for more detail.
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%)
 |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%)
 template instantiation             :   0.27 ( 29%)   0.08 ( 35%)   0.89 ( 36%)    25M ( 32%)
 TOTAL                              :   0.93          0.23          2.50           79M
Compiler time reports are most useful if you understand compiler internals. For general use, Ninja log analysis is recommended.

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Clang -ftime-report

Clang also supports -ftime-report flag with similar functionality.

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Runtime Profiling

SerenityOS includes a built-in profiler for analyzing application and system performance.

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The profile Command

The profile command records profiling information that can be viewed with ProfileViewer.

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Basic Usage

# Profile a running process by PID
profile -p 42

# Profile a command
profile echo "Hello friends!"

# Enable whole-system profiling (requires superuser)
profile -ae

# ...do work...

# Stop profiling
profile -ad
Results are saved to /sys/kernel/profile.
Track specific event types with the -t flag:
# Profile syscalls
profile -t syscall -- echo "Hello friends!"

# Profile page faults
profile -t page_fault -- ./my-app

# Profile context switches
profile -t context_switch -- ./my-app
Available event types:
  • sample - Sampling events
  • context_switch - Context switches
  • page_fault - Page faults
  • syscall - System calls
  • read - Read operations
  • kmalloc - Kernel memory allocations
  • kfree - Kernel memory frees

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Options

OptionDescription
-p PIDTarget specific process ID
-aProfile all processes (super-user only)
-eEnable profiling
-dDisable profiling
-fFree the profiling buffer
-wEnable profiling and wait for user input to disable
-t event_typeTrack specific event type

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ProfileViewer

ProfileViewer is a GUI application for viewing profiling data produced by profile. Launch it from the Applications menu or command line: 
Profiler
It provides:
  • Flame graphs of execution time
  • Call tree analysis
  • Timeline views
  • Per-function statistics

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Performance Tips

For accurate profiling results:
  • Use release builds (-DCMAKE_BUILD_TYPE=Release)
  • Disable debug macros that add logging overhead
  • Profile on real hardware when possible, as VM performance varies
On Linux, QEMU is significantly faster with KVM. Ensure /dev/kvm exists and is readable/writable by your user.

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See Also

  • Debugging - Debugging tools and techniques
  • Testing - Running and debugging tests
  • strace - System call tracer

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