--- a/net/minecraft/Util.java
+++ b/net/minecraft/Util.java
@@ -92,9 +92,25 @@
     private static final int DEFAULT_MAX_THREADS = 255;
     private static final int DEFAULT_SAFE_FILE_OPERATION_RETRIES = 10;
     private static final String MAX_THREADS_SYSTEM_PROPERTY = "max.bg.threads";
-    private static final TracingExecutor BACKGROUND_EXECUTOR = makeExecutor("Main");
+    private static final TracingExecutor BACKGROUND_EXECUTOR = makeExecutor("Main", -1); // Paper - Perf: add priority
     private static final TracingExecutor IO_POOL = makeIoExecutor("IO-Worker-", false);
     private static final TracingExecutor DOWNLOAD_POOL = makeIoExecutor("Download-", true);
+    // Paper start - don't submit BLOCKING PROFILE LOOKUPS to the world gen thread
+    public static final ExecutorService PROFILE_EXECUTOR = Executors.newFixedThreadPool(2, new java.util.concurrent.ThreadFactory() {
+
+        private final AtomicInteger count = new AtomicInteger();
+
+        @Override
+        public Thread newThread(Runnable run) {
+            Thread ret = new Thread(run);
+            ret.setName("Profile Lookup Executor #" + this.count.getAndIncrement());
+            ret.setUncaughtExceptionHandler((Thread thread, Throwable throwable) -> {
+                LOGGER.error("Uncaught exception in thread " + thread.getName(), throwable);
+            });
+            return ret;
+        }
+    });
+    // Paper end - don't submit BLOCKING PROFILE LOOKUPS to the world gen thread
     private static final DateTimeFormatter FILENAME_DATE_TIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd_HH.mm.ss", Locale.ROOT);
     public static final int LINEAR_LOOKUP_THRESHOLD = 8;
     private static final Set<String> ALLOWED_UNTRUSTED_LINK_PROTOCOLS = Set.of("http", "https");
@@ -136,7 +152,7 @@
     }
 
     public static long getNanos() {
-        return timeSource.getAsLong();
+        return System.nanoTime(); // Paper
     }
 
     public static long getEpochMillis() {
@@ -147,15 +163,16 @@
         return FILENAME_DATE_TIME_FORMATTER.format(ZonedDateTime.now());
     }
 
-    private static TracingExecutor makeExecutor(String name) {
+    private static TracingExecutor makeExecutor(String name, final int priorityModifier) { // Paper - Perf: add priority
         int i = maxAllowedExecutorThreads();
-        ExecutorService executorService;
+        // Paper start - Perf: use simpler thread pool that allows 1 thread and reduce worldgen thread worker count for low core count CPUs
+        final ExecutorService executorService;
         if (i <= 0) {
             executorService = MoreExecutors.newDirectExecutorService();
         } else {
-            AtomicInteger atomicInteger = new AtomicInteger(1);
-            executorService = new ForkJoinPool(i, pool -> {
-                final String string2 = "Worker-" + name + "-" + atomicInteger.getAndIncrement();
+            executorService = Executors.newFixedThreadPool(i, target -> new io.papermc.paper.util.ServerWorkerThread(target, name, priorityModifier));
+        }
+        /*      final String string2 = "Worker-" + name + "-" + atomicInteger.getAndIncrement();
                 ForkJoinWorkerThread forkJoinWorkerThread = new ForkJoinWorkerThread(pool) {
                     @Override
                     protected void onStart() {
@@ -177,13 +194,26 @@
                 forkJoinWorkerThread.setName(string2);
                 return forkJoinWorkerThread;
             }, Util::onThreadException, true);
-        }
+        }*/
 
         return new TracingExecutor(executorService);
     }
 
     public static int maxAllowedExecutorThreads() {
-        return Mth.clamp(Runtime.getRuntime().availableProcessors() - 1, 1, getMaxThreads());
+        // Paper start - Perf: use simpler thread pool that allows 1 thread and reduce worldgen thread worker count for low core count CPUs
+        final int cpus = Runtime.getRuntime().availableProcessors() / 2;
+        int maxExecutorThreads;
+        if (cpus <= 4) {
+            maxExecutorThreads = cpus <= 2 ? 1 : 2;
+        } else if (cpus <= 8) {
+            // [5, 8]
+            maxExecutorThreads = Math.max(3, cpus - 2);
+        } else {
+            maxExecutorThreads = cpus * 2 / 3;
+        }
+        maxExecutorThreads = Math.min(8, maxExecutorThreads);
+        return Integer.getInteger("Paper.WorkerThreadCount", maxExecutorThreads);
+        // Paper end - Perf: use simpler thread pool that allows 1 thread and reduce worldgen thread worker count for low core count CPUs
     }
 
     private static int getMaxThreads() {
@@ -537,7 +567,7 @@
     public static <K extends Enum<K>, V> EnumMap<K, V> makeEnumMap(Class<K> enumClass, Function<K, V> mapper) {
         EnumMap<K, V> enumMap = new EnumMap<>(enumClass);
 
-        for (K enum_ : (Enum[])enumClass.getEnumConstants()) {
+        for (K enum_ : enumClass.getEnumConstants()) { // Paper - decompile error
             enumMap.put(enum_, mapper.apply(enum_));
         }
 
@@ -1057,16 +1087,7 @@
         }
 
         public void openUri(URI uri) {
-            try {
-                Process process = AccessController.doPrivileged(
-                    (PrivilegedExceptionAction<Process>)(() -> Runtime.getRuntime().exec(this.getOpenUriArguments(uri)))
-                );
-                process.getInputStream().close();
-                process.getErrorStream().close();
-                process.getOutputStream().close();
-            } catch (IOException | PrivilegedActionException var3) {
-                Util.LOGGER.error("Couldn't open location '{}'", uri, var3);
-            }
+            throw new IllegalStateException("This method is not useful on dedicated servers."); // Paper - Fix warnings on build by removing client-only code
         }
 
         public void openFile(File file) {