From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <spottedleaf@spottedleaf.dev>
Date: Sat, 4 Apr 2020 17:00:20 -0700
Subject: [PATCH] Consolidate flush calls for entity tracker packets

Most server packets seem to be sent from here, so try to avoid
expensive flush calls from them.

This change was motivated due to local testing:

- My server spawn has 130 cows in it (for testing a prev. patch)
- Try to let 200 players join spawn

Without this change, I could only get 20 players on before they
all started timing out due to the load put on the Netty I/O threads.

With this change I could get all 200 on at 0ms ping.

(one of the primary issues is that my CPU is kinda trash, and having
4 extra threads at 100% is just too much for it).

So in general this patch should reduce Netty I/O thread load.

diff --git a/src/main/java/net/minecraft/server/level/ServerChunkCache.java b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
index d7ec783caebd71364c1c3a414bcf1aac271b0574..7470f3ba66c2e894b5a5b0ba392ecabf8b04aff9 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -1069,7 +1069,24 @@ public class ServerChunkCache extends ChunkSource {
             this.level.getProfiler().pop();
         }
 
+        // Paper start - controlled flush for entity tracker packets
+        List<net.minecraft.network.Connection> disabledFlushes = new java.util.ArrayList<>(this.level.players.size());
+        for (ServerPlayer player : this.level.players) {
+            net.minecraft.server.network.ServerGamePacketListenerImpl connection = player.connection;
+            if (connection != null) {
+                connection.connection.disableAutomaticFlush();
+                disabledFlushes.add(connection.connection);
+            }
+        }
+        try { // Paper end - controlled flush for entity tracker packets
         this.chunkMap.tick();
+        // Paper start - controlled flush for entity tracker packets
+        } finally {
+            for (net.minecraft.network.Connection networkManager : disabledFlushes) {
+                networkManager.enableAutomaticFlush();
+            }
+        }
+        // Paper end - controlled flush for entity tracker packets
     }
 
     private void getFullChunk(long pos, Consumer<LevelChunk> chunkConsumer) {