build-parallelism

MSBuild Parallelism Model /maxcpucount (or -m ): number of worker nodes (processes) Default: 1 node (sequential!). Always use -m for parallel builds Recommended: -m without a number = use all logical processors Each node builds one project at a time Projects are scheduled based on dependency graph Project Dependency Graph MSBuild builds projects in dependency order (topological sort) Critical path: longest chain of dependent projects determines minimum build time Bottleneck: if project A depends on B, C, D and B takes 60s while C and D take 5s, B is the bottleneck Diagnosis: replay binlog to diagnostic log with performancesummary and check Project Performance Summary — shows per-project time; grep for node.*assigned to check scheduling Wide graphs (many independent projects) parallelize well; deep graphs (long chains) don't Graph Build Mode ( /graph ) dotnet build /graph or msbuild /graph What it changes: MSBuild constructs the full project dependency graph BEFORE building Benefits: better scheduling, avoids redundant evaluations, enables isolated builds Limitations: all projects must use (no programmatic MSBuild task references) When to use: large solutions with many projects, CI builds When NOT to use: projects that dynamically discover references at build time Optimizing Project References Reduce unnecessary — each adds to the dependency chain Use to avoid extra evaluations for build-order-only dependencies Consider if a ProjectReference should be a PackageReference instead (pre-built NuGet) Use solution filters ( .slnf ) to build subsets of the solution BuildInParallel in custom targets Without BuildInParallel="true" , MSBuild task batches projects sequentially Ensure /maxcpucount

1 for this to have effect Multi-threaded MSBuild Tasks Individual tasks can run multi-threaded within a single project build Tasks implementing IMultiThreadableTask can run on multiple threads Tasks must declare thread-safety via [MSBuildMultiThreadableTask] Analyzing Parallelism with Binlog Step-by-step: Replay the binlog: dotnet msbuild build.binlog -noconlog -fl -flp:v=diag;logfile=full.log;performancesummary Check Project Performance Summary at the end of full.log Ideal: build time should be much less than sum of project times (parallelism) If build time ≈ sum of project times: too many serial dependencies, or one slow project blocking others grep 'Target Performance Summary' -A 30 full.log → find the bottleneck targets Consider splitting large projects or optimizing the critical path CI/CD Parallelism Tips Use -m in CI (many CI runners have multiple cores) Consider splitting solution into build stages for extreme parallelism Use build caching (NuGet lock files, deterministic builds) to avoid rebuilding unchanged projects dotnet build /graph works well with structured CI pipelines