Drop fewer packets on UDP packet flood (#5565)

* ACK received-but-unprocessed packets when queued

* Prioritize packets between high- and low-priority (high-priority are: reliable packets that need an ACK)

* Increase max size of LLPacketRing buffer

1 files changed, 35 insertions, 44 deletions

diff --git a/indra/newview/llappviewer.cpp b/indra/newview/llappviewer.cpp
index 79752d2315..7f06f991b0 100644
--- a/indra/newview/llappviewer.cpp
+++ b/indra/newview/llappviewer.cpp
@@ -5894,7 +5894,6 @@ void LLAppViewer::idleNetwork()
     pingMainloopTimeout("idleNetwork");
 
     gObjectList.mNumNewObjects = 0;
-    S32 total_decoded = 0;
 
     static LLCachedControl<bool> speed_test(gSavedSettings, "SpeedTest", false);
     if (!speed_test())
@@ -5902,64 +5901,56 @@ void LLAppViewer::idleNetwork()
         LL_PROFILE_ZONE_NAMED_CATEGORY_NETWORK("idle network"); //LL_RECORD_BLOCK_TIME(FTM_IDLE_NETWORK); // decode
 
         LLTimer check_message_timer;
-        //  Read all available packets from network
         const S64 frame_count = gFrameCount;  // U32->S64
-        F32 total_time = 0.0f;
+        S32 total_decoded = 0;
 
+        // Process packets from network
+        LockMessageChecker lmc(gMessageSystem);
+        while (lmc.checkAllMessages(frame_count, gServicePump))
         {
-            bool needs_drain = false;
-            LockMessageChecker lmc(gMessageSystem);
-            while (lmc.checkAllMessages(frame_count, gServicePump))
-            {
-                if (gDoDisconnect)
-                {
-                    // We're disconnecting, don't process any more messages from the server
-                    // We're usually disconnecting due to either network corruption or a
-                    // server going down, so this is OK.
-                    break;
-                }
-
-                total_decoded++;
+            ++total_decoded;
 
-                if (total_decoded > MESSAGE_MAX_PER_FRAME)
+            // Time-box processing of network packets to prevent framerate catastrophe
+            if (check_message_timer.getElapsedTimeF32() >= CheckMessagesMaxTime)
+            {
+                // Drain the socket buffer so we know how many messages remain to process
+                S32 num_buffered_packets = gMessageSystem->drainUdpSocket();
+                if (num_buffered_packets > total_decoded)
                 {
-                    needs_drain = true;
-                    break;
+                    // Grow CheckMessagesMaxTime until we process more packets each frame than arrive.
+                    // This might spiral out of control on very slow computers on fast networks when
+                    // the bandwidth settings are too high.  There is a mechanism for providing backpressure
+                    // to network bandwidth but it may be inadequate for the task
+                    // (see LLViewerThrottle::updateDynamicThrottle() for more details).
+                    CheckMessagesMaxTime *= 1.035f; // 3.5% ~= 2x in 20 frames, ~8x in 60 frames
                 }
-
-                // Prevent slow packets from completely destroying the frame rate.
-                // This usually happens due to clumps of avatars taking huge amount
-                // of network processing time (which needs to be fixed, but this is
-                // a good limit anyway).
-                total_time = check_message_timer.getElapsedTimeF32();
-                if (total_time >= CheckMessagesMaxTime)
+                else if (num_buffered_packets == 0)
                 {
-                    needs_drain = true;
-                    break;
+                    // Reset CheckMessagesMaxTime to default value
+                    CheckMessagesMaxTime = CHECK_MESSAGES_DEFAULT_MAX_TIME;
                 }
+                break;
             }
-            if (needs_drain || gMessageSystem->mPacketRing.getNumBufferedPackets() > 0)
+
+            if (total_decoded > MESSAGE_MAX_PER_FRAME)
             {
-                // Rather than allow packets to silently backup on the socket
-                // we drain them into our own buffer so we know how many exist.
-                S32 num_buffered_packets = gMessageSystem->drainUdpSocket();
-                if (num_buffered_packets > 0)
-                {
-                    // Increase CheckMessagesMaxTime so that we will eventually catch up
-                    CheckMessagesMaxTime *= 1.035f; // 3.5% ~= 2x in 20 frames, ~8x in 60 frames
-                }
+                // MESSAGE_MAX_PER_FRAME is very high (400)
+                // We expect to run out of time before reaching here, but just in case...
+                gMessageSystem->drainUdpSocket();
+                break;
             }
-            else
+
+            if (gDoDisconnect)
             {
-                // Reset CheckMessagesMaxTime to default value
-                CheckMessagesMaxTime = CHECK_MESSAGES_DEFAULT_MAX_TIME;
+                // We're disconnecting so no need to process packets.
+                break;
             }
+        }
 
-            // Handle per-frame message system processing.
+        // Handle per-frame message system processing.
 
-            static LLCachedControl<F32> ack_collection_time(gSavedSettings, "AckCollectTime", 0.1f);
-            lmc.processAcks(ack_collection_time());
-        }
+        static LLCachedControl<F32> ack_collection_time(gSavedSettings, "AckCollectTime", 0.1f);
+        lmc.processAcks(ack_collection_time());
     }
     add(LLStatViewer::NUM_NEW_OBJECTS, gObjectList.mNumNewObjects);