diff --git a/src/python/grpcio_tests/tests/qps/histogram.py b/src/python/grpcio_tests/tests/qps/histogram.py
index e0f06ffa9ec..8139a6ee2fb 100644
--- a/src/python/grpcio_tests/tests/qps/histogram.py
+++ b/src/python/grpcio_tests/tests/qps/histogram.py
@@ -67,7 +67,7 @@ class Histogram(object):
 
     def merge(self, another_data):
         with self._lock:
-            for i in len(self._buckets):
+            for i in range(len(self._buckets)):
                 self._buckets[i] += another_data.bucket[i]
             self._min = min(self._min, another_data.min_seen)
             self._max = max(self._max, another_data.max_seen)
diff --git a/src/python/grpcio_tests/tests_aio/benchmark/worker_servicer.py b/src/python/grpcio_tests/tests_aio/benchmark/worker_servicer.py
index f6bafd35703..ee72165019c 100644
--- a/src/python/grpcio_tests/tests_aio/benchmark/worker_servicer.py
+++ b/src/python/grpcio_tests/tests_aio/benchmark/worker_servicer.py
@@ -120,17 +120,20 @@ def _create_client(server: str, config: control_pb2.ClientConfig,
     return client_type(server, config, qps_data)
 
 
-WORKER_ENTRY_FILE = os.path.split(os.path.abspath(__file__))[0] + 'worker.py'
+WORKER_ENTRY_FILE = os.path.split(os.path.abspath(__file__))[0] + '/worker.py'
 SubWorker = collections.namedtuple('SubWorker', ['process', 'port', 'channel', 'stub'])
 
 
 async def _create_sub_worker(port: int) -> SubWorker:
-    process = asyncio.create_subprocess_exec(
+    process = await asyncio.create_subprocess_exec(
         sys.executable,
         WORKER_ENTRY_FILE,
-        '--driver_port', port
+        '--driver_port', str(port)
     )
+    _LOGGER.info('Created sub worker process for port [%d] at pid [%d]', port, process.pid)
     channel = aio.insecure_channel(f'localhost:{port}')
+    _LOGGER.info('Waiting for sub worker at port [%d]', port)
+    await aio.channel_ready(channel)
     stub = worker_service_pb2_grpc.WorkerServiceStub(channel)
     return SubWorker(
         process=process,
@@ -200,46 +203,54 @@ class WorkerServicer(worker_service_pb2_grpc.WorkerServiceServicer):
         config = config_request.setup
         _LOGGER.info('Received ClientConfig: %s', config)
 
-        if config.async_server_threads <= 0:
-            raise ValueError('async_server_threads can\'t be [%d]' % config.async_server_threads)
-        elif config.async_server_threads == 1:
+        if config.async_client_threads <= 0:
+            raise ValueError('async_client_threads can\'t be [%d]' % config.async_client_threads)
+        elif config.async_client_threads == 1:
             await self._run_single_client(config, request_iterator, context)
         else:
             sub_workers = []
-            for i in range(config.async_server_threads):
+            for i in range(config.async_client_threads):
                 port = 40000+i
                 _LOGGER.info('Creating sub worker at port [%d]...', port)
                 sub_workers.append(await _create_sub_worker(port))
 
             calls = [worker.stub.RunClient() for worker in sub_workers]
 
+            config_request.setup.async_client_threads = 1
+
             for call in calls:
                 await call.write(config_request)
+                # An empty status
+                await call.read()
 
             start_time = time.time()
             result = histogram.Histogram(config.histogram_params.resolution,
                                          config.histogram_params.max_possible)
             end_time = time.time()
-            yield _get_client_status(start_time, end_time, result)
+            await context.write(_get_client_status(start_time, end_time, result))
 
             async for request in request_iterator:
                 end_time = time.time()
 
                 for call in calls:
+                    _LOGGER.debug('Fetching status...')
                     await call.write(request)
                     sub_status = await call.read()
-                    result.merge(sub_status.latencies)
+                    result.merge(sub_status.stats.latencies)
+                    _LOGGER.debug('Update from sub worker count=[%d]', sub_status.stats.latencies.count)
 
                 status = _get_client_status(start_time, end_time, result)
                 if request.mark.reset:
                     result.reset()
                     start_time = time.time()
-                yield status
+                _LOGGER.debug('Reporting count=[%d]', status.stats.latencies.count)
+                await context.write(status)
 
             for call in calls:
-                await call.QuitWorker()
+                await call.done_writing()
 
             for worker in sub_workers:
+                await worker.stub.QuitWorker(control_pb2.Void())
                 await worker.channel.close()
                 _LOGGER.info('Waiting for sub worker [%s] to quit...', worker)
                 await worker.process.wait()
diff --git a/tools/run_tests/performance/scenario_config.py b/tools/run_tests/performance/scenario_config.py
index 5a4fddf16e6..e935539605c 100644
--- a/tools/run_tests/performance/scenario_config.py
+++ b/tools/run_tests/performance/scenario_config.py
@@ -838,7 +838,7 @@ class PythonAsyncIOLanguage:
             channels=1,
             client_threads_per_cq=1,
             server_threads_per_cq=1,
-            async_server_threads=6,
+            async_client_threads=7,
             unconstrained_client=True,
             categories=[SMOKETEST, SCALABLE])