diff --git a/libs/utils/analysis/frequency_analysis.py b/libs/utils/analysis/frequency_analysis.py
index 395e2ab..ddf098f 100644
--- a/libs/utils/analysis/frequency_analysis.py
+++ b/libs/utils/analysis/frequency_analysis.py
@@ -368,13 +368,13 @@
             logging.warn('Cluster frequency is NOT coherent,'
                          'cannot compute residency!')
             return None
-        cluster_freqs = freq_df[freq_df.cpu == _cluster[0]].frequency
+        cluster_freqs = freq_df[freq_df.cpu == _cluster[0]]
 
         # Compute TOTAL Time
         time_intervals = cluster_freqs.index[1:] - cluster_freqs.index[:-1]
         total_time = pd.DataFrame({
             'time': time_intervals,
-            'frequency': [f/1000.0 for f in cluster_freqs.iloc[:-1]]
+            'frequency': [f/1000.0 for f in cluster_freqs.iloc[:-1].frequency]
         })
         total_time = total_time.groupby(['frequency']).sum()
 
@@ -390,15 +390,14 @@
         # - freq_active, square wave of the form:
         #     freq_active[t] == 1 if at time t the frequency is f
         #     freq_active[t] == 0 otherwise
-        available_freqs = sorted(cluster_freqs.unique())
-        new_idx = sorted(cluster_freqs.index.tolist() +
-                         cluster_active.index.tolist())
-        cluster_freqs = cluster_freqs.reindex(new_idx, method='ffill')
-        cluster_active = cluster_active.reindex(new_idx, method='ffill')
+        available_freqs = sorted(cluster_freqs.frequency.unique())
+        cluster_freqs = cluster_freqs.join(
+            cluster_active.to_frame(name='active'), how='outer')
+        cluster_freqs.fillna(method='ffill', inplace=True)
         nonidle_time = []
         for f in available_freqs:
-            freq_active = cluster_freqs.apply(lambda x: 1 if x == f else 0)
-            active_t = cluster_active * freq_active
+            freq_active = cluster_freqs.frequency.apply(lambda x: 1 if x == f else 0)
+            active_t = cluster_freqs.active * freq_active
             # Compute total time by integrating the square wave
             nonidle_time.append(self._trace.integrate_square_wave(active_t))
 
diff --git a/libs/utils/trace.py b/libs/utils/trace.py
index 1c4440e..e1a94cb 100644
--- a/libs/utils/trace.py
+++ b/libs/utils/trace.py
@@ -788,11 +788,13 @@
                          'cannot compute cluster active signal!')
             return None
 
-        cpu_active = {}
-        for cpu in cluster:
-            cpu_active[cpu] = self.getCPUActiveSignal(cpu)
+        active = self.getCPUActiveSignal(cluster[0]).to_frame(name=cluster[0])
+        for cpu in cluster[1:]:
+            active = active.join(
+                self.getCPUActiveSignal(cpu).to_frame(name=cpu),
+                how='outer'
+            )
 
-        active = pd.DataFrame(cpu_active)
         active.fillna(method='ffill', inplace=True)
 
         # Cluster active is the OR between the actives on each CPU