Make UnaryCallOverheadBenchmark parametrized

src/csharp/Grpc.Microbenchmarks/UnaryCallOverheadBenchmark.cs

@@ -33,14 +33,28 @@ namespace Grpc.Microbenchmarks
     public class UnaryCallOverheadBenchmark
     {
         private static readonly Task<string> CompletedString = Task.FromResult("");
-        private static readonly byte[] EmptyBlob = new byte[0];
-        private static readonly Marshaller<string> EmptyMarshaller = new Marshaller<string>(_ => EmptyBlob, _ => "");
-        private static readonly Method<string, string> PingMethod = new Method<string, string>(MethodType.Unary, nameof(PingBenchmark), "Ping", EmptyMarshaller, EmptyMarshaller);
+        private static readonly Marshaller<byte[]> IdentityMarshaller = new Marshaller<byte[]>(msg => msg, payload => payload);
+        private static readonly Method<byte[], byte[]> PingMethod = new Method<byte[], byte[]>(MethodType.Unary, nameof(PingBenchmark), "Ping", IdentityMarshaller, IdentityMarshaller);
+
+        private int payloadSize;
+        private byte[] payload;
+
+        // size of payload that is sent as request and received as response.
+        [Params(0, 1, 10, 100, 1000)]
+        public int PayloadSize
+        {
+            get { return payloadSize; }
+            set
+            {
+                payloadSize = value;
+                payload = new byte[value];
+            }
+        }
 
         [Benchmark]
-        public string SyncUnaryCallOverhead()
+        public byte[] SyncUnaryCallOverhead()
         {
-            return client.Ping("", new CallOptions());
+            return client.Ping(payload, new CallOptions());
         }
 
         Channel channel;
@@ -81,7 +95,7 @@ namespace Grpc.Microbenchmarks
         {
             public PingClient(CallInvoker callInvoker) : base(callInvoker) { }
 
-            public string Ping(string request, CallOptions options)
+            public byte[] Ping(byte[] request, CallOptions options)
             {
                 return CallInvoker.BlockingUnaryCall(PingMethod, null, options, request);
             }