qemu-iotests: Extend iotest 093 to test bursts

This patch adds a new test that checks that the burst settings
('iops_max', 'iops_max_length', etc.) of the throttling code work as
expected.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/093

@@ -3,7 +3,7 @@
 # Tests for IO throttling
 #
 # Copyright (C) 2015 Red Hat, Inc.
-# Copyright (C) 2015 Igalia, S.L.
+# Copyright (C) 2015-2016 Igalia, S.L.
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -21,6 +21,8 @@
 
 import iotests
 
+nsec_per_sec = 1000000000
+
 class ThrottleTestCase(iotests.QMPTestCase):
     test_img = "null-aio://"
     max_drives = 3
@@ -42,16 +44,7 @@ class ThrottleTestCase(iotests.QMPTestCase):
     def tearDown(self):
         self.vm.shutdown()
 
-    def do_test_throttle(self, ndrives, seconds, params):
-        def check_limit(limit, num):
-            # IO throttling algorithm is discrete, allow 10% error so the test
-            # is more robust
-            return limit == 0 or \
-                   (num < seconds * limit * 1.1 / ndrives
-                   and num > seconds * limit * 0.9 / ndrives)
-
-        nsec_per_sec = 1000000000
-
+    def configure_throttle(self, ndrives, params):
         params['group'] = 'test'
 
         # Set the I/O throttling parameters to all drives
@@ -60,13 +53,21 @@ class ThrottleTestCase(iotests.QMPTestCase):
             result = self.vm.qmp("block_set_io_throttle", conv_keys=False, **params)
             self.assert_qmp(result, 'return', {})
 
+    def do_test_throttle(self, ndrives, seconds, params):
+        def check_limit(limit, num):
+            # IO throttling algorithm is discrete, allow 10% error so the test
+            # is more robust
+            return limit == 0 or \
+                   (num < seconds * limit * 1.1 / ndrives
+                   and num > seconds * limit * 0.9 / ndrives)
+
         # Set vm clock to a known value
         ns = seconds * nsec_per_sec
         self.vm.qtest("clock_step %d" % ns)
 
-        # Submit enough requests. They will drain bps_max and iops_max, but the
-        # rest requests won't get executed until we advance the virtual clock
-        # with qtest interface
+        # Submit enough requests so the throttling mechanism kicks
+        # in. The throttled requests won't be executed until we
+        # advance the virtual clock.
         rq_size = 512
         rd_nr = max(params['bps'] / rq_size / 2,
                     params['bps_rd'] / rq_size,
@@ -142,6 +143,42 @@ class ThrottleTestCase(iotests.QMPTestCase):
             for tk in params:
                 limits = dict([(k, 0) for k in params])
                 limits[tk] = params[tk] * ndrives
+                self.configure_throttle(ndrives, limits)
+                self.do_test_throttle(ndrives, 5, limits)
+
+    def test_burst(self):
+        params = {"bps": 4096,
+                  "bps_rd": 4096,
+                  "bps_wr": 4096,
+                  "iops": 10,
+                  "iops_rd": 10,
+                  "iops_wr": 10,
+                 }
+        ndrives = 1
+        # Pick each out of all possible params and test
+        for tk in params:
+            rate = params[tk] * ndrives
+            burst_rate = rate * 7
+            burst_length = 4
+
+            # Configure the throttling settings
+            settings = dict([(k, 0) for k in params])
+            settings[tk] = rate
+            settings['%s_max' % tk] = burst_rate
+            settings['%s_max_length' % tk] = burst_length
+            self.configure_throttle(ndrives, settings)
+
+            # Wait for the bucket to empty so we can do bursts
+            wait_ns = nsec_per_sec * burst_length * burst_rate / rate
+            self.vm.qtest("clock_step %d" % wait_ns)
+
+            # Test I/O at the max burst rate
+            limits = dict([(k, 0) for k in params])
+            limits[tk] = burst_rate
+            self.do_test_throttle(ndrives, burst_length, limits)
+
+            # Now test I/O at the normal rate
+            limits[tk] = rate
             self.do_test_throttle(ndrives, 5, limits)
 
 class ThrottleTestCoroutine(ThrottleTestCase):

tests/qemu-iotests/093.out

@@ -1,5 +1,5 @@
-..
+....
 ----------------------------------------------------------------------
-Ran 2 tests
+Ran 4 tests
 
 OK