Devide the #regions into separate C# files

src/benchmarks/micro/corefx/System.Threading.Tasks.Dataflow/Perf.ActionBlock.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Threading.Tasks.Dataflow.Tests
+{
+    public class ActionBlockPerfTests : TargetPerfTests<ITargetBlock<int>>
+    {
+        public override ITargetBlock<int> CreateBlock() => new ActionBlock<int>(i => { });
+    }
+
+    public class ParallelActionBlockPerfTests : TargetPerfTests<ITargetBlock<int>>
+    {
+        public override ITargetBlock<int> CreateBlock() =>
+            new ActionBlock<int>(
+                i => { },
+                new ExecutionDataflowBlockOptions
+                {
+                    MaxDegreeOfParallelism = Environment.ProcessorCount
+                }
+            );
+    }
+
+    public class UnorderedParallelActionBlockPerfTests : TargetPerfTests<ITargetBlock<int>>
+    {
+        public override ITargetBlock<int> CreateBlock() =>
+            new ActionBlock<int>(
+                i => { },
+                new ExecutionDataflowBlockOptions
+                {
+                    MaxDegreeOfParallelism = Environment.ProcessorCount,
+                    EnsureOrdered = false
+                }
+            );
+    }
+
+    public class SingleProducerConstrainedActionBlockPerfTests : TargetPerfTests<ITargetBlock<int>>
+    {
+        public override ITargetBlock<int> CreateBlock() =>
+            new ActionBlock<int>(
+                i => { },
+                new ExecutionDataflowBlockOptions
+                {
+                    SingleProducerConstrained = true
+                }
+            );
+    }
+}

src/benchmarks/micro/corefx/System.Threading.Tasks.Dataflow/Perf.BatchBlock.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Threading.Tasks.Dataflow.Tests
+{
+    public class BatchBlockPerfTests : PropagatorPerfTests<IPropagatorBlock<int, int[]>, int[]>
+    {
+        protected override int ReceiveSize { get; } = 100;
+        public override IPropagatorBlock<int, int[]> CreateBlock() => new BatchBlock<int>(ReceiveSize);
+    }
+}

src/benchmarks/micro/corefx/System.Threading.Tasks.Dataflow/Perf.BatchedJoinBlock.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using BenchmarkDotNet.Attributes;
+using MicroBenchmarks;
+
+namespace System.Threading.Tasks.Dataflow.Tests
+{
+    [BenchmarkCategory(Categories.CoreFX)]
+    public class BatchedJoinBlockPerfTests : SourceBlockPerfTests<BatchedJoinBlock<int, int>, Tuple<IList<int>, IList<int>>>
+    {
+        protected override int ReceiveSize { get; } = 100;
+
+        public override BatchedJoinBlock<int, int> CreateBlock() => new BatchedJoinBlock<int, int>(ReceiveSize);
+
+        [Benchmark(OperationsPerInvoke = 100_000)]
+        public async Task PostTwiceReceiveOnceParallel()
+        {
+            await Task.WhenAll(
+                Post(block.Target1),
+                Post(block.Target2),
+                Receive()
+            );
+        }
+
+        [Benchmark(OperationsPerInvoke = 100_000)]
+        public async Task SendAsyncTwiceReceiveAsyncOnceParallel()
+        {
+            await Task.WhenAll(
+                SendAsync(block.Target1),
+                SendAsync(block.Target2),
+                ReceiveAsync()
+            );
+        }
+    }
+}

src/benchmarks/micro/corefx/System.Threading.Tasks.Dataflow/Perf.BroadcastBlock.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using BenchmarkDotNet.Attributes;
+using MicroBenchmarks;
+
+namespace System.Threading.Tasks.Dataflow.Tests
+{
+    [BenchmarkCategory(Categories.CoreFX)]
+    public class BroadcastBlockPerfTests : PropagatorPerfTests<IPropagatorBlock<int, int>, int>
+    {
+        public override IPropagatorBlock<int, int> CreateBlock() =>
+            new BroadcastBlock<int>(
+                i => i,
+                new ExecutionDataflowBlockOptions
+                {
+                    MaxDegreeOfParallelism = Environment.ProcessorCount
+                });
+
+        [Benchmark(OperationsPerInvoke = 100_000)]
+        public Task PostMultiReceiveParallel() => MultiParallel(() => Post());
+
+        [Benchmark(OperationsPerInvoke = 100_000)]
+        public Task SendMultiReceiveAsyncParallel() => MultiParallel(() => SendAsync());
+
+        private async Task MultiParallel(Func<Task> doTask)
+        {
+            var options = new DataflowLinkOptions { PropagateCompletion = true };
+            var action1 = new ActionBlock<int>(i => { });
+            var action2 = new ActionBlock<int>(i => { });
+            block.LinkTo(action1, options);
+            block.LinkTo(action2, options);
+
+            await doTask();
+            block.Complete();
+
+            await Task.WhenAll(action1.Completion, action2.Completion);
+        }
+    }
+}

src/benchmarks/micro/corefx/System.Threading.Tasks.Dataflow/Perf.BufferBlock.cs

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+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace System.Threading.Tasks.Dataflow.Tests
+{
+    public class UnboundedBufferBlockPerfTests : PropagatorPerfTests<IPropagatorBlock<int, int>, int>
+    {
+        public override IPropagatorBlock<int, int> CreateBlock() => new BufferBlock<int>();
+    }
+
+    public class BoundedBufferBlockPerfTests : BoundedPropagatorPerfTests<IPropagatorBlock<int, int>, int>
+    {
+        public override IPropagatorBlock<int, int> CreateBlock() =>
+            new BufferBlock<int>(
+                new DataflowBlockOptions
+                {
+                    BoundedCapacity = 100
+                });
+    }
+}