PaperMC/patches/server/0768-Consolidate-flush-calls-for-entity-tracker-packets.patch

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 0d9f8180110b072e54d6c0f8c64df584b40776b9..758bb0fae0f9ba9672250e4a65c27f1175eab12d 100644
--- a/src/main/java/net/minecraft/server/level/ServerChunkCache.java
+++ b/src/main/java/net/minecraft/server/level/ServerChunkCache.java
@@ -1053,7 +1053,24 @@ public class ServerChunkCache extends ChunkSource {
             });
             gameprofilerfiller.pop();
             gameprofilerfiller.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
         }
     }