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

1 files changed, 36 insertions, 4 deletions

diff --git a/nova/weights.py b/nova/weights.py
index 97dc7d3291..75d51dc5f7 100644
--- a/nova/weights.py
+++ b/nova/weights.py
@@ -19,9 +19,14 @@ Pluggable Weighing support
 
 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.
 
@@ -128,13 +133,40 @@ class BaseWeightHandler(loadables.BaseLoader):
         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)