# UNDF: UNDF-2026-000001053
# UNDF: UNDF-2026-XXXXXXXXX
--- a/src/Ryujinx.HLE/HOS/Services/Sockets/Bsd/Impl/ManagedSocketPollManager.cs
+++ b/src/Ryujinx.HLE/HOS/Services/Sockets/Bsd/Impl/ManagedSocketPollManager.cs
@@ -1,6 +1,6 @@
 using Ryujinx.Common.Logging;
 using Ryujinx.HLE.HOS.Services.Sockets.Bsd.Types;
-using System.Collections.Generic;
+using System.Collections.Generic;
 using System.Net.Sockets;

 namespace Ryujinx.HLE.HOS.Services.Sockets.Bsd.Impl
@@ -71,13 +71,19 @@ namespace Ryujinx.HLE.HOS.Services.Sockets.Bsd.Impl
             try
             {
                 int actualTimeoutMicroseconds = timeoutMilliseconds == -1 ? -1 : timeoutMilliseconds * 1000;

                 Socket.Select(readEvents, writeEvents, errorEvents, actualTimeoutMicroseconds);
             }
             catch (SocketException exception)
             {
                 return WinSockHelper.ConvertError((WsaError)exception.ErrorCode);
             }

+            // Convert to HashSet after Socket.Select() trims each list to ready sockets.
+            // List.Contains() is O(S) per call; HashSet.Contains() is O(1).
+            // Without this, the result loop below is O(E * S) where E = event count,
+            // S = ready-socket count in each list. At E=500 sockets, cost is ~250,000 ops.
+            HashSet<Socket> readSet   = new(readEvents);
+            HashSet<Socket> writeSet  = new(writeEvents);
+            HashSet<Socket> errorSet  = new(errorEvents);
+
             foreach (PollEvent evnt in events)
             {
                 Socket socket = ((ManagedSocket)evnt.FileDescriptor).Socket;
@@ -85,17 +91,17 @@ namespace Ryujinx.HLE.HOS.Services.Sockets.Bsd.Impl
                 PollEventTypeMask outputEvents = evnt.Data.OutputEvents & ~evnt.Data.InputEvents;

-                if (errorEvents.Contains(socket))
+                if (errorSet.Contains(socket))
                 {
                     outputEvents |= PollEventTypeMask.Error;

                     if (!socket.Connected || !socket.IsBound)
                     {
                         outputEvents |= PollEventTypeMask.Disconnected;
                     }
                 }

-                if (readEvents.Contains(socket))
+                if (readSet.Contains(socket))
                 {
                     if ((evnt.Data.InputEvents & PollEventTypeMask.Input) != 0)
                     {
                         outputEvents |= PollEventTypeMask.Input;
                     }
                 }

-                if (writeEvents.Contains(socket))
+                if (writeSet.Contains(socket))
                 {
                     outputEvents |= PollEventTypeMask.Output;
                 }
@@ -119,6 +125,11 @@ namespace Ryujinx.HLE.HOS.Services.Sockets.Bsd.Impl

             Socket.Select(readEvents, writeEvents, errorEvents, timeout);

+            // Same O(E*S) -> O(E+S) fix for Select().
+            HashSet<Socket> readSet   = new(readEvents);
+            HashSet<Socket> writeSet  = new(writeEvents);
+            HashSet<Socket> errorSet  = new(errorEvents);
+
             updatedCount = readEvents.Count + writeEvents.Count + errorEvents.Count;

             foreach (PollEvent pollEvent in events)
@@ -126,15 +137,15 @@ namespace Ryujinx.HLE.HOS.Services.Sockets.Bsd.Impl
                 ManagedSocket socket = (ManagedSocket)pollEvent.FileDescriptor;

-                if (readEvents.Contains(socket.Socket))
+                if (readSet.Contains(socket.Socket))
                 {
                     pollEvent.Data.OutputEvents |= PollEventTypeMask.Input;
                 }

-                if (writeEvents.Contains(socket.Socket))
+                if (writeSet.Contains(socket.Socket))
                 {
                     pollEvent.Data.OutputEvents |= PollEventTypeMask.Output;
                 }

-                if (errorEvents.Contains(socket.Socket))
+                if (errorSet.Contains(socket.Socket))
                 {
                     pollEvent.Data.OutputEvents |= PollEventTypeMask.Error;
                 }