From 7f8d641501fe1bd71c989aab25ccbdb5ddb0726f Mon Sep 17 00:00:00 2001
From: Christoph Wille <christoph.wille@gmail.com>
Date: Sat, 15 Aug 2026 14:48:29 +0200
Subject: [PATCH 1/2] Use server GC for the decompiler test suite

The suite keeps one NUnit worker per logical CPU busy with allocation-heavy
decompiles (223 GB allocated per run), so under workstation GC every
gen0/gen1 collection any worker triggers suspends the whole process.
Measured on a 24-thread Windows box (Debug, ILSpy-tests checked out):
27,229 gen0 / 6,919 gen1 collections and 305 s of total GC pause in a
553 s run, at 45% average CPU. With server GC the same run takes 310 s,
1,251 gen0 / 492 gen1, 14 s of pause, 80% CPU, for the same ~46 min of
processor time; the in-suite roundtrip decompiles drop 2-3x
(Random_TestCase_1 353 s -> 133 s, ExplicitConversions 319 s -> 136 s,
NRefactory_CSharp 337 s -> 156 s). Standalone ilspycmd timings are
unaffected, which is what pointed at contention inside the test process
rather than decompiler cost.

Assisted-by: Claude:claude-fable-5:Claude Code
---
 .../ICSharpCode.Decompiler.Tests.csproj                     | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj b/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj
index 58ebff48bd..714454f75b 100644
--- a/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj
+++ b/ICSharpCode.Decompiler.Tests/ICSharpCode.Decompiler.Tests.csproj
@@ -18,6 +18,12 @@
 
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
 
+    <!-- The suite runs dozens of allocation-heavy decompiles concurrently (one NUnit worker per
+         logical CPU, each roundtrip adding WholeProjectDecompiler's own Parallel.ForEach). Workstation
+         GC stops the whole process for every gen0/gen1 collection any worker triggers; measured on a
+         24-thread machine that was ~300 s of pause in a ~550 s run. Server GC gives each core its own
+         heap and collects in parallel. -->
+    <ServerGarbageCollection>true</ServerGarbageCollection>
     <!-- NU1902/1903 are "Package 'X' has a known security vulnerability". In our tests, we don't care. -->
     <!-- CA1416 fires because the TFM dropped its -windows suffix: Windows-only helpers (SdkUtility,
          Tester.SignAssembly/FindMSBuild/RunWithTestRunner) and Windows-only test inputs (Console.CapsLock

From 1ddd5986ae485121c212785b3e83ee60ac7290b4 Mon Sep 17 00:00:00 2001
From: Christoph Wille <christoph.wille@gmail.com>
Date: Sat, 15 Aug 2026 16:20:32 +0200
Subject: [PATCH 2/2] Run the Windows CI test step under workstation GC

The Windows job runs every test host of the solution concurrently on a
4-core runner. With ICSharpCode.Decompiler.Tests on server GC that host
sits at 98-100% CPU for the whole test step, and the neighbours starve:
the process-module walk in ILSpy.Tests.Windows exceeded its 60 s budget
(OperationCanceledException in NetFrameworkProcessesTests, Release job),
a background sampler measured its own walk over the ~170 runner processes
at 40-170 s instead of a few seconds, and ILSpy.Tests took 685 s instead
of 375 s (Release). Memory was not the constraint: never below 9 GB free,
disk idle. The decompiler suite itself moved little on that box (Debug
1393 s -> 1226 s, Release 664 s -> 751 s). Server GC stays on for machines
the suite has to itself; the Linux job runs the projects one at a time.

Assisted-by: Claude:claude-fable-5:Claude Code
---
 .github/workflows/build-ilspy.yml | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/.github/workflows/build-ilspy.yml b/.github/workflows/build-ilspy.yml
index 8b786ab0e2..3249f3b650 100644
--- a/.github/workflows/build-ilspy.yml
+++ b/.github/workflows/build-ilspy.yml
@@ -99,6 +99,13 @@ jobs:
 
     - name: Execute unit tests
       id: unit-tests
+      # All test hosts of the solution run concurrently on a 4-core runner. Server GC (enabled by
+      # ICSharpCode.Decompiler.Tests for machines it has to itself) keeps that host at 100% CPU
+      # and starves the neighbours: the process-module walks in ILSpy.Tests.Windows blow their
+      # 60 s budget and ILSpy.Tests takes almost twice as long, while the decompiler suite itself
+      # gains little here. The environment variable overrides the runtimeconfig setting.
+      env:
+        DOTNET_gcServer: 0
       run: >
         dotnet test --solution ilspy.sln
         --configuration ${{ matrix.configuration }}