Build Performance Baseline & Optimization

Overview

Before optimizing a build, you need a baseline. Without measurements, optimization is guesswork. This skill covers how to establish baselines and apply systematic optimization techniques.

Related skills:

• build-perf-diagnostics — binlog-based bottleneck identification

• incremental-build — Inputs/Outputs and up-to-date checks

• build-parallelism — parallel and graph build tuning

• eval-performance — glob and import chain optimization

Step 1: Establish a Performance Baseline

Measure three scenarios to understand where time is spent:

Cold Build (First Build)

No previous build output exists. Measures the full end-to-end time including restore, compilation, and all targets.

Clean everything first

dotnet clean

Remove bin/obj to truly start fresh

Get-ChildItem -Recurse -Directory -Include bin,obj | Remove-Item -Recurse -Force

OR on Linux/macOS:

find . -type d ( -name bin -o -name obj ) -exec rm -rf {} +

Measure cold build

dotnet build /bl:cold-build.binlog -m

Warm Build (Incremental Build)

Build output exists, some files have changed. Measures how well incremental build works.

Build once to populate outputs

dotnet build -m

Make a small change (touch one .cs file)

Then rebuild

dotnet build /bl:warm-build.binlog -m

No-Op Build (Nothing Changed)

Build output exists, nothing has changed. This should be nearly instant. If it's slow, incremental build is broken.

Build once to populate outputs

dotnet build -m

Rebuild immediately without changes

dotnet build /bl:noop-build.binlog -m

What Good Looks Like

Scenario Expected Behavior

Cold build Full compilation, all targets run. This is your absolute baseline

Warm build Only changed projects recompile. Time proportional to change scope

No-op build < 5 seconds for small repos, < 30 seconds for large repos. All compilation targets should report "Skipping target — all outputs up-to-date"

Red flags:

• No-op build > 30 seconds → incremental build is broken (see incremental-build skill)

• Warm build recompiles everything → project dependency chain forces full rebuild

• Cold build has long restore → NuGet cache issues

Recording Baselines

Record baselines in a structured way before and after optimization:

Step 2: MSBuild Server (Persistent Build Process)

The MSBuild server keeps the build process alive between invocations, avoiding JIT compilation and assembly loading overhead on every build.

Enabling MSBuild Server

Enabled by default in .NET 8+ but can be forced

dotnet build /p:UseSharedCompilation=true

The MSBuild server is started automatically and reused across builds. The compiler server (VBCSCompiler / dotnet build-server ) is separate but complementary.

Managing the Build Server

Check if the server is running

dotnet build-server status

Shut down all build servers (useful when debugging)

dotnet build-server shutdown

When to Restart the Build Server

Restart after:

• Updating the .NET SDK

• Changing MSBuild tooling (custom tasks, props, targets)

• Debugging build infrastructure issues

• Seeing stale behavior in repeated builds

dotnet build-server shutdown dotnet build

Step 3: Artifacts Output Layout

The UseArtifactsOutput feature (introduced in .NET 8) changes the output directory structure to avoid bin/obj clash issues and enable better caching.

Enabling Artifacts Output

<!-- Directory.Build.props --> <PropertyGroup> <UseArtifactsOutput>true</UseArtifactsOutput> </PropertyGroup>

Before vs After

Traditional layout (before)

src/ MyLib/ bin/Debug/net8.0/MyLib.dll obj/Debug/net8.0/... MyApp/ bin/Debug/net8.0/MyApp.dll

Artifacts layout (after)

artifacts/ bin/MyLib/debug/MyLib.dll bin/MyApp/debug/MyApp.dll obj/MyLib/debug/... obj/MyApp/debug/...

Benefits

• No bin/obj clash: Each project+configuration gets a unique path automatically

• Easier to cache: Single artifacts/ directory to cache/restore in CI

• Cleaner .gitignore: Just ignore artifacts/

• Multi-targeting safe: Each TFM gets its own subdirectory

Customizing

<!-- Change the artifacts root --> <PropertyGroup> <ArtifactsPath>$(MSBuildThisFileDirectory)output</ArtifactsPath> </PropertyGroup>

Step 4: Deterministic Builds

Deterministic builds produce byte-for-byte identical output given the same inputs. This is essential for build caching and reproducibility.

Enabling Deterministic Builds

<!-- Directory.Build.props --> <PropertyGroup> <!-- Enabled by default in .NET SDK projects since SDK 2.0+ --> <Deterministic>true</Deterministic>

<!-- For full reproducibility, also set: --> <ContinuousIntegrationBuild Condition="'$(CI)' == 'true'">true</ContinuousIntegrationBuild> </PropertyGroup>

What Deterministic Affects

• Removes timestamps from PE headers

• Uses consistent file paths in PDBs

• Produces identical output for identical input

Why It Matters for Performance

• Build caching: If outputs are deterministic, you can cache and reuse them across builds and machines

• CI optimization: Skip rebuilding unchanged projects by comparing inputs

• Distributed builds: Safe to cache compilation results in shared storage

Step 5: Dependency Graph Trimming

Reducing unnecessary project references shortens the critical path and reduces what gets built.

Audit the Dependency Graph

Visualize the dependency graph

dotnet build /bl:graph.binlog

In the binlog, check project references and build times

Look for projects that are referenced but could be trimmed

Techniques

Remove Redundant Transitive References

<!-- BAD: Utils is already referenced transitively via Core --> <ItemGroup> <ProjectReference Include="..\Core\Core.csproj" /> <ProjectReference Include="..\Utils\Utils.csproj" /> </ItemGroup>

<!-- GOOD: Let transitive references flow automatically --> <ItemGroup> <ProjectReference Include="..\Core\Core.csproj" /> </ItemGroup>

Build-Order-Only References

When you need a project to build before yours but don't need its assembly output:

<!-- Only ensures build order, doesn't reference the output assembly --> <ProjectReference Include="..\CodeGen\CodeGen.csproj" ReferenceOutputAssembly="false" />

Prevent Transitive Flow

When a dependency is an internal implementation detail that shouldn't flow to consumers:

<!-- Don't expose this dependency transitively --> <ProjectReference Include="..\InternalHelpers\InternalHelpers.csproj" PrivateAssets="all" />

Disable Transitive Project References

For explicit-only dependency management (extreme measure for very large repos):

<PropertyGroup> <DisableTransitiveProjectReferences>true</DisableTransitiveProjectReferences> </PropertyGroup>

Caution: This requires all dependencies to be listed explicitly. Only use in large repos where transitive closure is causing excessive rebuilds.

Step 6: Static Graph Builds (/graph )

Static graph mode evaluates the entire project graph before building, enabling better scheduling and isolation.

Enabling Graph Build

Single invocation

dotnet build /graph

With binary log for analysis

dotnet build /graph /bl:graph-build.binlog

Benefits

• Better parallelism: MSBuild knows the full graph upfront and can schedule optimally

• Build isolation: Each project builds in isolation (no cross-project state leakage)

• Caching potential: With isolation, individual project results can be cached

When to Use

Scenario Recommendation

Large multi-project solution (20+ projects) ✅ Try /graph — may see significant parallelism gains

Small solution (< 5 projects) ❌ Overhead of graph evaluation outweighs benefits

CI builds ✅ Graph builds are more predictable and parallelizable

Local development ⚠️ Test both — may or may not help depending on project structure

Troubleshooting Graph Build

Graph build requires that all ProjectReference items are statically determinable (no dynamic references computed in targets). If graph build fails:

error MSB4260: Project reference "..." could not be resolved with static graph.

Fix: Ensure all ProjectReference items are declared in <ItemGroup> outside of targets (not dynamically computed inside <Target> blocks).

Step 7: Parallel Build Tuning

MaxCpuCount

Use all available cores (default in dotnet build)

dotnet build -m

Specify explicit core count (useful for CI with shared agents)

dotnet build -m:4

MSBuild.exe syntax

msbuild /m:8 MySolution.sln

Identifying Parallelism Bottlenecks

In a binlog, look for:

• Long sequential chains: Projects that must build one after another due to dependencies

• Uneven load: Some build nodes idle while others are overloaded

• Single-project bottleneck: One large project on the critical path that blocks everything

Use grep 'Target Performance Summary' -A 30 full.log in binlog analysis to see build node utilization.

Reducing the Critical Path

The critical path is the longest chain of dependent projects. To shorten it:

• Break large projects into smaller ones that can build in parallel

• Remove unnecessary ProjectReferences (see Step 5)

• Use ReferenceOutputAssembly="false" for build-order-only dependencies

• Move shared code to a base library that builds first, then parallelize consumers

Step 8: Additional Quick Wins

Separate Restore from Build

In CI, restore once then build without restore

dotnet restore dotnet build --no-restore -m dotnet test --no-build

Skip Unnecessary Targets

Skip building documentation

dotnet build /p:GenerateDocumentationFile=false

Skip analyzers during development (not for CI!)

dotnet build /p:RunAnalyzers=false

Use Project-Level Filtering

Build only the project you're working on (and its dependencies)

dotnet build src/MyApp/MyApp.csproj

Don't build the entire solution if you only need one project

Binary Log for All Investigations

Always start with a binlog:

dotnet build /bl:perf.binlog -m

Then use the build-perf-diagnostics skill and binlog tools for systematic bottleneck identification.

Optimization Decision Tree

Is your no-op build slow (> 10s per project)? ├── YES → See incremental-build skill (fix Inputs/Outputs) └── NO Is your cold build slow? ├── YES │ Is restore slow? │ ├── YES → Optimize NuGet restore (use lock files, configure local cache) │ └── NO │ Is compilation slow? │ ├── YES │ │ Are analyzers/generators slow? │ │ ├── YES → See build-perf-diagnostics skill │ │ └── NO → Check parallelism, graph build, critical path (this skill + build-parallelism) │ └── NO → Check custom targets (binlog analysis via build-perf-diagnostics) └── NO Is your warm build slow? ├── YES → Projects rebuilding unnecessarily → check incremental-build skill └── NO → Build is healthy! Consider graph build or UseArtifactsOutput for further gains