add utf-8 encode benchmark

src/csharp/Grpc.Core.Tests/Properties/AssemblyInfo.cs

@@ -27,3 +27,9 @@ using System.Runtime.CompilerServices;
 [assembly: AssemblyCopyright("Google Inc.  All rights reserved.")]
 [assembly: AssemblyTrademark("")]
 [assembly: AssemblyCulture("")]
+
+[assembly: InternalsVisibleTo("Grpc.Microbenchmarks,PublicKey=" +
+    "00240000048000009400000006020000002400005253413100040000010001002f5797a92c6fcde81bd4098f43" +
+    "0442bb8e12768722de0b0cb1b15e955b32a11352740ee59f2c94c48edc8e177d1052536b8ac651bce11ce5da3a" +
+    "27fc95aff3dc604a6971417453f9483c7b5e836756d5b271bf8f2403fe186e31956148c03d804487cf642f8cc0" +
+    "71394ee9672dfe5b55ea0f95dfd5a7f77d22c962ccf51320d3")]

src/csharp/Grpc.Microbenchmarks/Grpc.Microbenchmarks.csproj

@@ -11,6 +11,7 @@
 
   <ItemGroup>
     <ProjectReference Include="../Grpc.Core/Grpc.Core.csproj" />
+    <ProjectReference Include="../Grpc.Core.Tests/Grpc.Core.Tests.csproj" />
   </ItemGroup>
 
   <ItemGroup>

src/csharp/Grpc.Microbenchmarks/Utf8Encode.cs

@@ -0,0 +1,72 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using BenchmarkDotNet.Attributes;
+using Grpc.Core;
+using Grpc.Core.Internal;
+using Grpc.Core.Internal.Tests;
+
+namespace Grpc.Microbenchmarks
+{
+    [ClrJob, CoreJob] // test .NET Core and .NET Framework
+    [MemoryDiagnoser] // allocations
+    public class Utf8Encode : ISendStatusFromServerCompletionCallback
+    {
+        static readonly NativeMethods Native = NativeMethods.Get();
+
+        [Params(0, 1, 4, 128, 1024)]
+        public int PayloadSize { get; set; }
+
+        static readonly Dictionary<int, string> Payloads = new Dictionary<int, string> {
+            { 0, Invent(0) },
+            { 1, Invent(1) },
+            { 4, Invent(4) },
+            { 128, Invent(128) },
+            { 1024, Invent(1024) },
+        };
+
+        static string Invent(int length)
+        {
+            var rand = new Random(Seed: length);
+            var chars = new char[length];
+            for(int i = 0; i < chars.Length; i++)
+            {
+                chars[i] = (char)rand.Next(32, 300);
+            }
+            return new string(chars);
+        }
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            Native.grpcsharp_test_override_method("grpcsharp_call_start_batch", "nop");
+            metadata = MetadataArraySafeHandle.Create(Metadata.Empty);
+            call = new FakeNativeCall();
+        }
+
+        public void Cleanup()
+        {
+            metadata.Dispose();
+            metadata = null;
+            call.Dispose();
+            call = null;
+        }
+        private INativeCall call;
+        private MetadataArraySafeHandle metadata;
+
+        const int Iterations = 1000;
+        [Benchmark(OperationsPerInvoke = Iterations)]
+        public unsafe void Run()
+        {
+            string payload = Payloads[PayloadSize];
+            var status = new Status(StatusCode.OK, payload);
+            for (int i = 0; i < Iterations; i++)
+            {
+                call.StartSendStatusFromServer(this, status,
+                    metadata, false, null, WriteFlags.NoCompress);
+            }
+        }
+
+        void ISendStatusFromServerCompletionCallback.OnSendStatusFromServerCompletion(bool success) { }
+    }
+}