Fix wrong CPU metric value in metrics_filter

CPU metrics are reported as a normalized value in [0,1].
When scheduler reads the data as MonitorMetric object, as part
of update_from_compute_node(), the value of the metric gets
lost due to a wrong type conversion, typecasting into an Integer,
reduces it to 0.

Note:
 - It may seem unintuitive that to fix the same, we are not changing
   the type of metric from Integer to Float. Please refer the
   discussions -
   * https://review.openstack.org/#/c/243825/
   * https://review.openstack.org/#/c/216923/
 - To summarize, we are trying to save some 'possible' downstream consumer
   of metrics updates from compute nodes, i.e. consuming from AMPQ, from
   software upgrade scenarios.

Change-Id: Ib504af33e05dfc4d7e97b52682e27befc67d784a
Closes-bug: #1514997
(cherry picked from commit ddb3c4e26f3a908de7836a8fac48360afa6aa1d7)

1 files changed, 12 insertions, 2 deletions

diff --git a/nova/objects/monitor_metric.py b/nova/objects/monitor_metric.py
index 7d6c350a41..0ad599b366 100644
--- a/nova/objects/monitor_metric.py
+++ b/nova/objects/monitor_metric.py
@@ -97,8 +97,18 @@ class MonitorMetricList(base.ObjectListBase, base.NovaObject):
         :returns: a MonitorMetricList Object.
         """
         metrics = jsonutils.loads(metrics) if metrics else []
-        metric_list = [
-            MonitorMetric(**metric) for metric in metrics]
+
+        # NOTE(suro-patz): While instantiating the MonitorMetric() from
+        #                  JSON-ified string, we need to re-convert the
+        #                  normalized metrics to avoid truncation to 0 by
+        #                  typecasting into an integer.
+        metric_list = []
+        for metric in metrics:
+            if ('value' in metric and metric['name'] in
+                                      FIELDS_REQUIRING_CONVERSION):
+                metric['value'] = metric['value'] * 100
+            metric_list.append(MonitorMetric(**metric))
+
         return MonitorMetricList(objects=metric_list)
 
     # NOTE(jaypipes): This method exists to convert the object to the