[To metric branch] Add benchmarks for targeting Exemplar impact

test/Benchmarks/Metrics/ExemplarBenchmarks.cs

@@ -0,0 +1,93 @@
+// <copyright file="ExemplarBenchmarks.cs" company="OpenTelemetry Authors">
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+// </copyright>
+
+using System.Diagnostics;
+using System.Diagnostics.Metrics;
+using BenchmarkDotNet.Attributes;
+using OpenTelemetry;
+using OpenTelemetry.Metrics;
+using OpenTelemetry.Tests;
+
+/*
+// * Summary *
+BenchmarkDotNet=v0.13.3, OS=Windows 11 (10.0.22621.1265)
+11th Gen Intel Core i7-1185G7 3.00GHz, 1 CPU, 8 logical and 4 physical cores
+.NET SDK=7.0.103
+  [Host]     : .NET 7.0.3 (7.0.323.6910), X64 RyuJIT AVX2
+  DefaultJob : .NET 7.0.3 (7.0.323.6910), X64 RyuJIT AVX2
+
+
+|          Method | EnableExemplar |     Mean |   Error |  StdDev | Allocated |
+|---------------- |--------------- |---------:|--------:|--------:|----------:|
+| HistogramUpdate |          False | 249.6 ns | 4.42 ns | 7.13 ns |         - |
+| HistogramUpdate |           True | 284.2 ns | 5.39 ns | 5.04 ns |         - |
+
+*/
+
+namespace Benchmarks.Metrics
+{
+    public class ExemplarBenchmarks
+    {
+        private static readonly ThreadLocal<Random> ThreadLocalRandom = new(() => new Random());
+        private readonly string[] dimensionValues = new string[] { "DimVal1", "DimVal2", "DimVal3", "DimVal4", "DimVal5", "DimVal6", "DimVal7", "DimVal8", "DimVal9", "DimVal10" };
+        private Histogram<long> histogram;
+        private MeterProvider provider;
+        private Meter meter;
+
+        [Params(true, false)]
+        public bool EnableExemplar { get; set; }
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            this.meter = new Meter(Utils.GetCurrentMethodName());
+            this.histogram = this.meter.CreateHistogram<long>("histogram");
+            var exportedItems = new List<Metric>();
+
+            this.provider = Sdk.CreateMeterProviderBuilder()
+                .AddMeter(this.meter.Name)
+                .SetExemplarFilter(this.EnableExemplar ? new AlwaysOnExemplarFilter() : new AlwaysOffExemplarFilter())
+                .AddInMemoryExporter(exportedItems, metricReaderOptions =>
+                {
+                    metricReaderOptions.PeriodicExportingMetricReaderOptions.ExportIntervalMilliseconds = 1000;
+                })
+                .Build();
+        }
+
+        [GlobalCleanup]
+        public void Cleanup()
+        {
+            this.meter?.Dispose();
+            this.provider?.Dispose();
+        }
+
+        [Benchmark]
+        public void HistogramUpdate()
+        {
+            var random = ThreadLocalRandom.Value;
+            var tags = new TagList
+            {
+                { "DimName1", this.dimensionValues[random.Next(0, 2)] },
+                { "DimName2", this.dimensionValues[random.Next(0, 2)] },
+                { "DimName3", this.dimensionValues[random.Next(0, 5)] },
+                { "DimName4", this.dimensionValues[random.Next(0, 5)] },
+                { "DimName5", this.dimensionValues[random.Next(0, 10)] },
+            };
+
+            this.histogram.Record(random.Next(1000), tags);
+        }
+    }
+}