| name | rsbuild-performance-profiling |
| description | Use when profiling, analyzing, reporting, or optimizing Rsbuild performance, including build, dev server, rebuild, static asset serving, memory usage, and CPU profile analysis. |
Rsbuild Performance Profiling
Workflow
-
Define the target scenario before collecting data:
- operation: build, dev startup, rebuild, request serving, memory usage, or another explicit flow
- benchmark project or fixture
- metric: wall time, CPU time, self time, allocations, RSS, heap
- success threshold, if the user provided one
-
Record the baseline first. Keep runtime, package manager, dependencies, environment variables, command flags, and input project unchanged for comparisons.
-
Save raw artifacts when available, such as CPU profiles, heap snapshots, logs, timing output, and benchmark commands. Do not rely only on subjective observations.
-
Separate costs by ownership:
- Rsbuild code paths
- Rspack or loader/plugin internals
- third-party dependencies
- user project code or benchmark fixture code
-
Rank findings by measured impact. Prefer self time for direct optimization targets and total time for understanding call-chain impact.
-
If implementing an optimization, keep behavior unchanged unless the user explicitly asked for a behavior change. Prefer small, measurable changes over broad refactors.
-
Re-run the same benchmark after changes. Report before/after numbers, absolute delta, percentage delta, and any variance or confidence limits you can observe.
Analysis Rules
- Treat the user's supplied profiles, reports, and benchmark numbers as the source of truth for that task.
- Do not claim a performance win without comparable before/after measurements.
- Do not optimize generated output, dependencies, or benchmark fixture code unless the user asked for that scope.
- For CPU profiles, call out both hot functions and why they are on the hot path.
- For memory tasks, distinguish peak usage from stable usage after warmup or repeated rebuilds.
Output
Return a concise report with:
- benchmark command or data source
- top findings ordered by impact
- Rsbuild-owned optimization opportunities
- changes made, if any
- validation results and remaining risk
