diff --git a/build.gradle b/build.gradle
index 9da4ae5757..f3f16d4eb4 100644
--- a/build.gradle
+++ b/build.gradle
@@ -54,7 +54,7 @@ targetCompatibility = JavaVersion.VERSION_1_6
 def junitVersion = "4.12"
 def reactiveStreamsVersion = "1.0.2"
 def mockitoVersion = "2.1.0"
-def jmhLibVersion = "1.19"
+def jmhLibVersion = "1.20"
 def testNgVersion = "6.11"
 def guavaVersion = "24.0-jre"
 def jacocoVersion = "0.8.0"
@@ -201,6 +201,7 @@ jmh {
     jmhVersion = jmhLibVersion
     humanOutputFile = null
     includeTests = false
+    jvmArgsAppend = ["-Djmh.separateClasspathJAR=true"]
 
     if (project.hasProperty("jmh")) {
         include = ".*" + project.jmh + ".*"
diff --git a/src/jmh/java/io/reactivex/FlowableFlatMapCompletablePerf.java b/src/jmh/java/io/reactivex/FlowableFlatMapCompletablePerf.java
new file mode 100644
index 0000000000..ec846d35eb
--- /dev/null
+++ b/src/jmh/java/io/reactivex/FlowableFlatMapCompletablePerf.java
@@ -0,0 +1,73 @@
+/**
+ * Copyright (c) 2016-present, RxJava Contributors.
+ *
+ * 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.
+ */
+
+package io.reactivex;
+
+import java.util.Arrays;
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.*;
+import org.openjdk.jmh.infra.Blackhole;
+
+import io.reactivex.functions.Action;
+import io.reactivex.internal.functions.Functions;
+import io.reactivex.schedulers.Schedulers;
+
+@BenchmarkMode(Mode.Throughput)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
+@OutputTimeUnit(TimeUnit.SECONDS)
+@Fork(value = 1)
+@State(Scope.Thread)
+public class FlowableFlatMapCompletablePerf implements Action {
+
+    @Param({"1", "10", "100", "1000", "10000", "100000", "1000000"})
+    int items;
+
+    @Param({"1", "8", "32", "128", "256"})
+    int maxConcurrency;
+
+    @Param({"1", "10", "100", "1000"})
+    int work;
+
+    Completable flatMapCompletable;
+
+    Flowable<Object> flatMap;
+
+    @Override
+    public void run() throws Exception {
+        Blackhole.consumeCPU(work);
+    }
+
+    @Setup
+    public void setup() {
+        Integer[] array = new Integer[items];
+        Arrays.fill(array, 777);
+
+        flatMapCompletable = Flowable.fromArray(array)
+                .flatMapCompletable(Functions.justFunction(Completable.fromAction(this).subscribeOn(Schedulers.computation())), false, maxConcurrency);
+
+        flatMap = Flowable.fromArray(array)
+                .flatMap(Functions.justFunction(Completable.fromAction(this).subscribeOn(Schedulers.computation()).toFlowable()), false, maxConcurrency);
+    }
+
+//    @Benchmark
+    public Object flatMap(Blackhole bh) {
+        return flatMap.subscribeWith(new PerfAsyncConsumer(bh)).await(items);
+    }
+
+    @Benchmark
+    public Object flatMapCompletable(Blackhole bh) {
+        return flatMapCompletable.subscribeWith(new PerfAsyncConsumer(bh)).await(items);
+    }
+}
diff --git a/src/jmh/java/io/reactivex/FlowableFlatMapCompletableSyncPerf.java b/src/jmh/java/io/reactivex/FlowableFlatMapCompletableSyncPerf.java
new file mode 100644
index 0000000000..047bad30a3
--- /dev/null
+++ b/src/jmh/java/io/reactivex/FlowableFlatMapCompletableSyncPerf.java
@@ -0,0 +1,63 @@
+/**
+ * Copyright (c) 2016-present, RxJava Contributors.
+ *
+ * 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.
+ */
+
+package io.reactivex;
+
+import java.util.Arrays;
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.*;
+import org.openjdk.jmh.infra.Blackhole;
+
+import io.reactivex.internal.functions.Functions;
+
+@BenchmarkMode(Mode.Throughput)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5, time = 1, timeUnit = TimeUnit.SECONDS)
+@OutputTimeUnit(TimeUnit.SECONDS)
+@Fork(value = 1)
+@State(Scope.Thread)
+public class FlowableFlatMapCompletableSyncPerf {
+
+    @Param({"1", "10", "100", "1000", "10000", "100000", "1000000"})
+    int items;
+
+    @Param({"1", "8", "32", "128", "256"})
+    int maxConcurrency;
+
+    Completable flatMapCompletable;
+
+    Flowable<Object> flatMap;
+
+    @Setup
+    public void setup() {
+        Integer[] array = new Integer[items];
+        Arrays.fill(array, 777);
+
+        flatMapCompletable = Flowable.fromArray(array)
+                .flatMapCompletable(Functions.justFunction(Completable.complete()), false, maxConcurrency);
+
+        flatMap = Flowable.fromArray(array)
+                .flatMap(Functions.justFunction(Completable.complete().toFlowable()), false, maxConcurrency);
+    }
+
+    @Benchmark
+    public Object flatMap(Blackhole bh) {
+        return flatMap.subscribeWith(new PerfConsumer(bh));
+    }
+
+    @Benchmark
+    public Object flatMapCompletable(Blackhole bh) {
+        return flatMapCompletable.subscribeWith(new PerfConsumer(bh));
+    }
+}
diff --git a/src/jmh/java/io/reactivex/PerfAsyncConsumer.java b/src/jmh/java/io/reactivex/PerfAsyncConsumer.java
index 8db609b4b5..0b99202afc 100644
--- a/src/jmh/java/io/reactivex/PerfAsyncConsumer.java
+++ b/src/jmh/java/io/reactivex/PerfAsyncConsumer.java
@@ -68,8 +68,9 @@ public void onComplete() {
     /**
      * Wait for the terminal signal.
      * @param count if less than 1001, a spin-wait is used
+     * @return this
      */
-    public void await(int count) {
+    public PerfAsyncConsumer await(int count) {
         if (count <= 1000) {
             while (getCount() != 0) { }
         } else {
@@ -79,6 +80,7 @@ public void await(int count) {
                 throw new RuntimeException(ex);
             }
         }
+        return this;
     }
 
 }
diff --git a/src/test/java/io/reactivex/internal/operators/flowable/FlowableFlatMapCompletableTest.java b/src/test/java/io/reactivex/internal/operators/flowable/FlowableFlatMapCompletableTest.java
index c91e7b8ef9..d132f56f7b 100644
--- a/src/test/java/io/reactivex/internal/operators/flowable/FlowableFlatMapCompletableTest.java
+++ b/src/test/java/io/reactivex/internal/operators/flowable/FlowableFlatMapCompletableTest.java
@@ -25,6 +25,7 @@
 import io.reactivex.disposables.*;
 import io.reactivex.exceptions.*;
 import io.reactivex.functions.Function;
+import io.reactivex.internal.functions.Functions;
 import io.reactivex.internal.fuseable.*;
 import io.reactivex.observers.*;
 import io.reactivex.processors.PublishProcessor;
@@ -523,4 +524,21 @@ public CompletableSource apply(Integer v) throws Exception {
         .test()
         .assertFailure(TestException.class);
     }
+
+    @Test
+    public void asyncMaxConcurrency() {
+        for (int itemCount = 1; itemCount <= 100000; itemCount *= 10) {
+            for (int concurrency = 1; concurrency <= 256; concurrency *= 2) {
+                Flowable.range(1, itemCount)
+                .flatMapCompletable(
+                        Functions.justFunction(Completable.complete()
+                        .subscribeOn(Schedulers.computation()))
+                        , false, concurrency)
+                .test()
+                .withTag("itemCount=" + itemCount + ", concurrency=" + concurrency)
+                .awaitDone(5, TimeUnit.SECONDS)
+                .assertResult();
+            }
+        }
+    }
 }