Adds flag --experimental_dynamic_execution_cpu_limited that prevent…

…s doing more dynamic execution threads than we have CPUs for.

Spinning up many threads and their various actions can take serious time, we have seen up to 18% slowdown. This limits the number of threads, improving cold build time while keeping the improvements for incremental builds. The downside is that with this, remote timeouts are much less likely to be avoided by the local finishing first.

PiperOrigin-RevId: 415474342

src/main/java/com/google/devtools/build/lib/dynamic/BUILD

@@ -14,11 +14,13 @@ java_library(
     name = "dynamic",
     srcs = glob(["*.java"]),
     deps = [
+        "//src/main/java/com/google/devtools/build/lib:build-request-options",
         "//src/main/java/com/google/devtools/build/lib:runtime",
         "//src/main/java/com/google/devtools/build/lib/actions",
         "//src/main/java/com/google/devtools/build/lib/actions:execution_requirements",
         "//src/main/java/com/google/devtools/build/lib/concurrent",
         "//src/main/java/com/google/devtools/build/lib/events",
+        "//src/main/java/com/google/devtools/build/lib/exec:execution_options",
         "//src/main/java/com/google/devtools/build/lib/exec:execution_policy",
         "//src/main/java/com/google/devtools/build/lib/exec:spawn_strategy_registry",
         "//src/main/java/com/google/devtools/build/lib/util:abrupt_exit_exception",

src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionModule.java

@@ -24,6 +24,7 @@
 import com.google.devtools.build.lib.actions.Spawn;
 import com.google.devtools.build.lib.actions.SpawnStrategy;
 import com.google.devtools.build.lib.actions.Spawns;
+import com.google.devtools.build.lib.buildtool.BuildRequestOptions;
 import com.google.devtools.build.lib.buildtool.BuildResult;
 import com.google.devtools.build.lib.buildtool.buildevent.BuildCompleteEvent;
 import com.google.devtools.build.lib.concurrent.ExecutorUtil;
@@ -133,18 +134,25 @@ private ImmutableMap<String, List<String>> getRemoteStrategies(DynamicExecutionO
   public void registerSpawnStrategies(
       SpawnStrategyRegistry.Builder registryBuilder, CommandEnvironment env)
       throws AbruptExitException {
+    DynamicExecutionOptions options = env.getOptions().getOptions(DynamicExecutionOptions.class);
+    com.google.devtools.build.lib.exec.ExecutionOptions execOptions =
+        env.getOptions().getOptions(com.google.devtools.build.lib.exec.ExecutionOptions.class);
     registerSpawnStrategies(
         registryBuilder,
-        env.getOptions().getOptions(DynamicExecutionOptions.class),
-        env.getReporter());
+        options,
+        env.getReporter(),
+        options.cpuLimited
+            ? (int) execOptions.localCpuResources
+            : env.getOptions().getOptions(BuildRequestOptions.class).jobs);
   }
 
   // CommandEnvironment is difficult to access in tests, so use this method for testing.
   @VisibleForTesting
   final void registerSpawnStrategies(
       SpawnStrategyRegistry.Builder registryBuilder,
       DynamicExecutionOptions options,
-      Reporter reporter)
+      Reporter reporter,
+      int numCpus)
       throws AbruptExitException {
     if (!options.internalSpawnScheduler) {
       return;
@@ -156,7 +164,8 @@ final void registerSpawnStrategies(
             options,
             this::getExecutionPolicy,
             this::getPostProcessingSpawnForLocalExecution,
-            firstBuild);
+            firstBuild,
+            numCpus);
     registryBuilder.registerStrategy(strategy, "dynamic", "dynamic_worker");
     registryBuilder.addDynamicLocalStrategies(getLocalStrategies(options));
     registryBuilder.addDynamicRemoteStrategies(getRemoteStrategies(options));

src/main/java/com/google/devtools/build/lib/dynamic/DynamicExecutionOptions.java

@@ -53,6 +53,16 @@ public class DynamicExecutionOptions extends OptionsBase {
               + "enabled.")
   public boolean internalSpawnScheduler;
 
+  @Option(
+      name = "experimental_dynamic_execution_cpu_limited",
+      documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
+      effectTags = {OptionEffectTag.UNKNOWN},
+      defaultValue = "false",
+      help =
+          "If true, the number of parallel dynamic executions is limited to the number of CPUs. "
+              + "The number of CPUs available can be set with the --local_cpu_resources flag.")
+  public boolean cpuLimited;
+
   @Option(
       name = "dynamic_local_strategy",
       converter = Converters.StringToStringListConverter.class,