Simplify the QoS bandwidth test to increase reliability

The initial implementation was measuring the bandwidth stability
over segments of time. But recent failures on high gate pressure
has shown that such stability can't be expected on the edge.

The test now checks the average bandwidth during the whole transmission.

Change-Id: Ic6a00f20ce76aba319ecdada79f68599c891cf29
Closes-Bug: #1662109

neutron/tests/tempest/scenario/test_qos.py

@@ -38,7 +38,6 @@ def _try_connect(host_ip, port):
         client_socket = socket.socket(socket.AF_INET,
                                       socket.SOCK_STREAM)
         client_socket.connect((host_ip, port))
-        client_socket.setblocking(0)
         return client_socket
     except socket.error as serr:
         if serr.errno == errno.ECONNREFUSED:
@@ -97,10 +96,6 @@ class QoSTest(base.BaseTempestTestCase):
                 file=QoSTest.FILE_PATH)
 
     def _check_bw(self, ssh_client, host, port):
-        total_bytes_read = 0
-        cycle_start_time = time.time()
-        cycle_data_read = 0
-
         cmd = "killall -q nc"
         try:
             ssh_client.exec_command(cmd)
@@ -109,36 +104,26 @@ class QoSTest(base.BaseTempestTestCase):
         cmd = ("(nc -ll -p %(port)d < %(file_path)s > /dev/null &)" % {
                 'port': port, 'file_path': QoSTest.FILE_PATH})
         ssh_client.exec_command(cmd)
+
+        start_time = time.time()
         client_socket = _connect_socket(host, port)
+        total_bytes_read = 0
 
         while total_bytes_read < QoSTest.FILE_SIZE:
-            try:
+            data = client_socket.recv(QoSTest.BUFFER_SIZE)
-                data = client_socket.recv(QoSTest.BUFFER_SIZE)
-            except socket.error as e:
-                if e.args[0] in [errno.EAGAIN, errno.EWOULDBLOCK]:
-                    continue
-                else:
-                    raise
             total_bytes_read += len(data)
-            cycle_data_read += len(data)
-            time_elapsed = time.time() - cycle_start_time
-            should_check = (time_elapsed >= 5 or
-                            total_bytes_read == QoSTest.FILE_SIZE)
-            if should_check:
-                LOG.debug("time_elapsed =  %(time_elapsed)d,"
-                          "total_bytes_read = %(bytes_read)d,"
-                          "cycle_data_read = %(cycle_data)d",
-                          {"time_elapsed": time_elapsed,
-                           "bytes_read": total_bytes_read,
-                           "cycle_data": cycle_data_read})
 
-                if cycle_data_read / time_elapsed > QoSTest.LIMIT_BYTES_SEC:
+        time_elapsed = time.time() - start_time
-                    # Limit reached
+        bytes_per_second = total_bytes_read / time_elapsed
-                    return False
+
-                else:
+        LOG.debug("time_elapsed = %(time_elapsed)d, "
-                    cycle_start_time = time.time()
+                  "total_bytes_read = %(total_bytes_read)d, "
-                    cycle_data_read = 0
+                  "bytes_per_second = %(bytes_per_second)d",
-        return True
+                  {'time_elapsed': time_elapsed,
+                   'total_bytes_read': total_bytes_read,
+                   'bytes_per_second': bytes_per_second})
+
+        return bytes_per_second <= QoSTest.LIMIT_BYTES_SEC
 
     @test.idempotent_id('1f7ed39b-428f-410a-bd2b-db9f465680df')
     def test_qos(self):