[Feature] Added diff calculation of stored values

Made changes in `SensorManager` to allow calculation of the difference in measured
(stored) values using `rapl_reader` functions

See Issue #12

nrm/coolr/clr_rapl.py

@@ -142,10 +142,12 @@ class rapl_reader:
             ret[k] = dvals
         return ret
 
-    def diffenergy(self,e1,e2): # e1 is prev and e2 is not
+    def diffenergy(self,e1,e2,shortenFlag=False): # e1 is prev and e2 is not
         ret = {}
         ret['time'] = e2['time'] - e1['time']
         for k in self.max_energy_range_uj_d:
+            if shortenFlag:
+                k = self.shortenkey(k)
             if e2[k]>=e1[k]:
                 ret[k] = e2[k] - e1[k]
             else:
@@ -155,7 +157,7 @@ class rapl_reader:
     # calculate the average power from two energy values
     # e1 and e2 are the value returned from readenergy()
     # e1 should be sampled before e2
-    def calcpower(self,e1,e2): 
+    def calcpower(self,e1,e2,shortenFlag=False): 
         ret = {}
         delta = e2['time'] - e1['time']  # assume 'time' never wrap around
         ret['delta']  = delta
@@ -166,6 +168,8 @@ class rapl_reader:
             return ret
 
         for k in self.max_energy_range_uj_d:
+            if shortenFlag:
+                k = self.shortenkey(k)
             if e2[k]>=e1[k]:
                 ret[k] = e2[k] - e1[k]
             else:

nrm/sensor.py

@@ -6,6 +6,7 @@
     This module should be the only one interfacing with coolr.
 """
 from __future__ import print_function
+import time
 import coolr
 import coolr.clr_rapl
 import coolr.clr_hwmon
@@ -33,6 +34,7 @@ class SensorManager:
         machine_info = dict()
         machine_info['energy'] = self.rapl.sample(accflag=True)
         machine_info['temperature'] = self.coretemp.sample()
+        machine_info['time'] = time.time()
         return machine_info
 
     def get_powerlimits(self):
@@ -42,3 +44,22 @@ class SensorManager:
 
     def set_powerlimit(self, domain, value):
         self.rapl.set_powerlimit(value, domain)
+
+    def calc_difference(self, start, end):
+        diff = dict()
+        # Calculate energy difference
+        diff['energy'] = self.rapl.diffenergy(start, end, shortenFlag=True)
+        # Update time elapsed
+        diff['time'] = diff['energy']['time']
+        # Remove 'time' field returned by function
+        diff['energy'].pop('time')
+        # Convert uJ to J
+        diff['energy'] = {k: diff['energy'][k]/(1000000.0) for k in
+                          diff['energy']}
+
+        # Calculate power difference
+        diff['power'] = self.rapl.calcpower(start, end, shortenFlag=True)
+        # Remove 'delta' field returned by function
+        diff['power'].pop('delta')
+
+        return diff