Add effective CPU overcommitment as derived node parameter

Add a derived parameter for nodes, providing the ratio of
virtual CPUs per CPU-speed weighted physical CPU.
Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>

src/Ganeti/HTools/Node.hs

@@ -28,6 +28,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 module Ganeti.HTools.Node
   ( Node(..)
   , List
+  , pCpuEff
   -- * Constructor
   , create
   -- ** Finalization after data loading
@@ -167,6 +168,11 @@ instance T.Element Node where
   setIdx = setIdx
   allNames n = [name n, alias n]
 
+-- | Derived parameter: ratio of virutal to pysical CPUs, weighted
+-- by CPU speed.
+pCpuEff :: Node -> Double
+pCpuEff n = pCpu n / tCpuSpeed n
+
 -- | A simple name for the int, node association list.
 type AssocList = [(T.Ndx, Node)]