Network thread count defaults

src/Microsoft.AspNet.Server.Kestrel/KestrelServer.cs

@@ -75,14 +75,37 @@ namespace Microsoft.AspNet.Server.Kestrel
                 _disposables.Push(engine);
                 _disposables.Push(dateHeaderValueManager);
 
+                // Actual core count would be a better number 
+                // rather than logical cores which includes hyper-threaded cores.
+                // Divide by 2 for hyper-threading, and good defaults (still need threads to do webserving).
+                // Can be user overriden using IKestrelServerInformation.ThreadCount
+                var threadCount = Environment.ProcessorCount >> 1;
+
+                if (threadCount < 1)
+                {
+                    // Ensure shifted value is at least one
+                    threadCount = 1;
+                }
+                else if (threadCount > 16)
+                {
+                    // Receive Side Scaling RSS Processor count currently maxes out at 16
+                    // would be better to check the NIC's current hardware queues; but xplat...
+                    threadCount = 16;
+                }
+
                 if (information.ThreadCount < 0)
                 {
                     throw new ArgumentOutOfRangeException(nameof(information.ThreadCount),
                         information.ThreadCount,
                         "ThreadCount cannot be negative");
                 }
+                else if (information.ThreadCount > 0)
+                {
+                    // ThreadCount has been user set, use that value
+                    threadCount = information.ThreadCount;
+                }
 
-                engine.Start(information.ThreadCount == 0 ? 1 : information.ThreadCount);
+                engine.Start(threadCount);
                 var atLeastOneListener = false;
 
                 foreach (var address in information.Addresses)