--- a/net/minecraft/Util.java
+++ b/net/minecraft/Util.java
@@ -92,9 +_,26 @@
     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);
+    public static final TracingExecutor DIMENSION_DATA_IO_POOL = makeExtraIoExecutor("Dimension-Data-IO-Worker-"); // Paper - Separate dimension data IO pool
     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");
@@ -113,6 +_,7 @@
         .findFirst()
         .orElseThrow(() -> new IllegalStateException("No jar file system provider found"));
     private static Consumer<String> thePauser = string -> {};
+    public static final double COLLISION_EPSILON = 1.0E-7; // Paper - Check distance in entity interactions
 
     public static <K, V> Collector<Entry<? extends K, ? extends V>, ?, Map<K, V>> toMap() {
         return Collectors.toMap(Entry::getKey, Entry::getValue);
@@ -135,7 +_,7 @@
     }
 
     public static long getNanos() {
-        return timeSource.getAsLong();
+        return System.nanoTime(); // Paper
     }
 
     public static long getEpochMillis() {
@@ -146,9 +_,10 @@
         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 directExecutorService;
+        // Paper start - Perf: use simpler thread pool that allows 1 thread and reduce worldgen thread worker count for low core count CPUs
+        final ExecutorService directExecutorService;
         if (i <= 0) {
             directExecutorService = MoreExecutors.newDirectExecutorService();
         } else {
@@ -173,16 +_,30 @@
                         super.onTermination(throwOnTermination);
                     }
                 };
+                forkJoinWorkerThread.setPriority(Thread.NORM_PRIORITY + priorityModifier); // Paper - Deprioritize over main
                 forkJoinWorkerThread.setName(string);
                 return forkJoinWorkerThread;
-            }, Util::onThreadException, true);
+            }, Util::onThreadException, true, 0, Integer.MAX_VALUE, 1, null, 365, TimeUnit.DAYS); // Paper - do not expire threads
         }
 
         return new TracingExecutor(directExecutorService);
     }
 
     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() {
@@ -233,6 +_,21 @@
         }));
     }
 
+    // Paper start - Separate dimension data IO pool
+    private static TracingExecutor makeExtraIoExecutor(String namePrefix) {
+        AtomicInteger atomicInteger = new AtomicInteger(1);
+        return new TracingExecutor(Executors.newFixedThreadPool(4, runnable -> {
+            Thread thread = new Thread(runnable);
+            String string2 = namePrefix + atomicInteger.getAndIncrement();
+            TracyClient.setThreadName(string2, namePrefix.hashCode());
+            thread.setName(string2);
+            thread.setDaemon(false);
+            thread.setUncaughtExceptionHandler(Util::onThreadException);
+            return thread;
+        }));
+    }
+    // Paper end - Separate dimension data IO pool
+
     public static void throwAsRuntime(Throwable throwable) {
         throw throwable instanceof RuntimeException ? (RuntimeException)throwable : new RuntimeException(throwable);
     }
@@ -1075,16 +_,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) {