Merge pull request #27025 from Sanne/LowerIOThreads

Reduce the number of vert.x eventloops started by default

extensions/vertx-http/runtime/src/main/java/io/quarkus/vertx/http/runtime/VertxHttpRecorder.java

@@ -274,8 +274,7 @@ public static void startServerAfterFailedStart() {
             doServerStart(vertx, buildConfig, config, LaunchMode.DEVELOPMENT, new Supplier<Integer>() {
                 @Override
                 public Integer get() {
-                    return ProcessorInfo.availableProcessors()
-                            * 2; //this is dev mode, so the number of IO threads not always being 100% correct does not really matter in this case
+                    return ProcessorInfo.availableProcessors(); //this is dev mode, so the number of IO threads not always being 100% correct does not really matter in this case
                 }
             }, null, false);
         } catch (Exception e) {

extensions/vertx/deployment/src/test/java/io/quarkus/vertx/deployment/MessageConsumerContextTest.java

@@ -84,11 +84,7 @@ public void testRequestReply() throws InterruptedException {
                 })
                 .await().atMost(Duration.ofSeconds(3));
 
-        if (Runtime.getRuntime().availableProcessors() > 1) {
-            assertEquals(3, MessageConsumers.MESSAGES.size());
-        } else {
-            assertTrue(MessageConsumers.MESSAGES.size() >= 2);
-        }
+        assertTrue(MessageConsumers.MESSAGES.size() >= 2);
     }
 
     @ApplicationScoped

extensions/vertx/runtime/src/main/java/io/quarkus/vertx/core/runtime/VertxCoreRecorder.java

@@ -381,7 +381,10 @@ private static int calculateDefaultIOThreads() {
         //it's hard to say what this number should be, but it is also obvious
         //that for constrained environments we don't want a lot of event loops
         //lets start with 10mb and adjust as needed
-        int recommended = ProcessorInfo.availableProcessors() * 2;
+        //We used to recommend a default of twice the number of cores,
+        //but more recent developments seem to suggest matching the number of cores 1:1
+        //being a more reasonable default. It also saves memory.
+        int recommended = ProcessorInfo.availableProcessors();
         long mem = Runtime.getRuntime().maxMemory();
         long memInMb = mem / (1024 * 1024);
         long maxAllowed = memInMb / 10;

extensions/vertx/runtime/src/main/java/io/quarkus/vertx/core/runtime/config/VertxConfiguration.java

@@ -23,7 +23,7 @@ public class VertxConfiguration {
     public boolean classpathResolving;
 
     /**
-     * The number of event loops. 2 x the number of core by default.
+     * The number of event loops. By default, it matches the number of CPUs detected on the system.
      */
     @ConfigItem
     public OptionalInt eventLoopsPoolSize;