Max I/O ops per host scheduler filter

Provide ability to filter hosts based on the number of concurrent
build, resize, and image snapshot operations in progress.

FLAGS.max_io_ops_per_host is used to control the number of concurrent
permitted operations.

Change-Id: I77feca00a6b6b248de8423cef7fb8da2cf704930

2 files changed, 60 insertions, 0 deletions

diff --git a/nova/scheduler/filters/io_ops_filter.py b/nova/scheduler/filters/io_ops_filter.py
new file mode 100644
index 000000000..c2e0205a3
--- /dev/null
+++ b/nova/scheduler/filters/io_ops_filter.py
@@ -0,0 +1,44 @@
+# Copyright (c) 2012 OpenStack, LLC.
+# All Rights Reserved.
+#
+#    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.
+
+from nova import flags
+from nova.openstack.common import cfg
+from nova.openstack.common import log as logging
+from nova.scheduler import filters
+
+LOG = logging.getLogger(__name__)
+
+max_io_ops_per_host_opt = cfg.IntOpt("max_io_ops_per_host",
+        default=8,
+        help="Ignore hosts that have too many builds/resizes/snaps/migrations")
+
+FLAGS = flags.FLAGS
+FLAGS.register_opt(max_io_ops_per_host_opt)
+
+
+class IoOpsFilter(filters.BaseHostFilter):
+    """Filter out hosts with too many concurrent I/O operations"""
+
+    def host_passes(self, host_state, filter_properties):
+        """Use information about current vm and task states collected from
+        compute node statistics to decide whether to filter.
+        """
+        num_io_ops = host_state.num_io_ops
+        max_io_ops = FLAGS.max_io_ops_per_host
+        passes = num_io_ops < max_io_ops
+        if not passes:
+            LOG.debug(_("%(host_state)s fails I/O ops check: Max IOs per host "
+                        "is set to %(max_io_ops)s"), locals())
+        return passes
diff --git a/nova/tests/scheduler/test_host_filters.py b/nova/tests/scheduler/test_host_filters.py
index 42d43a197..b1e1ec897 100644
--- a/nova/tests/scheduler/test_host_filters.py
+++ b/nova/tests/scheduler/test_host_filters.py
@@ -1278,3 +1278,19 @@ class HostFiltersTestCase(test.TestCase):
         retry = dict(num_attempts=1, hosts=['host3', 'host1'])
         filter_properties = dict(retry=retry)
         self.assertFalse(filt_cls.host_passes(host, filter_properties))
+
+    def test_filter_num_iops_passes(self):
+        self.flags(max_io_ops_per_host=8)
+        filt_cls = self.class_map['IoOpsFilter']()
+        host = fakes.FakeHostState('host1', 'compute',
+                                   {'num_io_ops': 7})
+        filter_properties = {}
+        self.assertTrue(filt_cls.host_passes(host, filter_properties))
+
+    def test_filter_num_iops_fails(self):
+        self.flags(max_io_ops_per_host=8)
+        filt_cls = self.class_map['IoOpsFilter']()
+        host = fakes.FakeHostState('host1', 'compute',
+                                   {'num_io_ops': 8})
+        filter_properties = {}
+        self.assertFalse(filt_cls.host_passes(host, filter_properties))