Add debug log for scheduler weight calculation

We have all the weighers enabled by default and each can have its own
multiplier making the final compute node order calculation pretty
complex. This patch adds some debug logging that helps understanding how
the final ordering was reached.

Change-Id: I7606d6eb3e08548c1df9dc245ab39cced7de1fb5
(cherry picked from commit 154ab7b)
(cherry picked from commit 30c7180)

Author: Balazs Gibizer

nova/weights.py

@@ -19,9 +19,14 @@
 
 import abc
 
+from oslo_log import log as logging
+
 from nova import loadables
 
 
+LOG = logging.getLogger(__name__)
+
+
 def normalize(weight_list, minval=None, maxval=None):
     """Normalize the values in a list between 0 and 1.0.
 
@@ -127,13 +132,40 @@ def get_weighed_objects(self, weighers, obj_list, weighing_properties):
         for weigher in weighers:
             weights = weigher.weigh_objects(weighed_objs, weighing_properties)
 
+            LOG.debug(
+                "%s: raw weights %s",
+                weigher.__class__.__name__,
+                {(obj.obj.host, obj.obj.nodename): weight
+                 for obj, weight in zip(weighed_objs, weights)}
+            )
+
             # Normalize the weights
-            weights = normalize(weights,
-                                minval=weigher.minval,
-                                maxval=weigher.maxval)
+            weights = list(
+                normalize(
+                    weights, minval=weigher.minval, maxval=weigher.maxval))
+
+            LOG.debug(
+                "%s: normalized weights %s",
+                weigher.__class__.__name__,
+                {(obj.obj.host, obj.obj.nodename): weight
+                 for obj, weight in zip(weighed_objs, weights)}
+            )
+
+            log_data = {}
 
             for i, weight in enumerate(weights):
                 obj = weighed_objs[i]
-                obj.weight += weigher.weight_multiplier(obj.obj) * weight
+                multiplier = weigher.weight_multiplier(obj.obj)
+                weigher_score = multiplier * weight
+                obj.weight += weigher_score
+
+                log_data[(obj.obj.host, obj.obj.nodename)] = (
+                    f"{multiplier} * {weight}")
+
+            LOG.debug(
+                "%s: score (multiplier * weight) %s",
+                weigher.__class__.__name__,
+                {name: log for name, log in log_data.items()}
+            )
 
         return sorted(weighed_objs, key=lambda x: x.weight, reverse=True)