Add decimal-cpu-percentage for CC stat usage.

[Finishes #120740573]

Signed-off-by: Sandy Cash <scarlet.tanager@gmail.com>

lib/dea/protocol.rb

@@ -56,7 +56,7 @@ def self.generate(bootstrap, instance, request)
           "fds_quota"  => instance.file_descriptor_limit,
           "usage"      => {
             "time" => Time.now.to_s,
-            "cpu"  => instance.stat_collector.computed_pcpu,
+            "cpu"  => instance.stat_collector.computed_dcpu,
             "mem"  => instance.stat_collector.used_memory_in_bytes,
             "disk" => instance.stat_collector.used_disk_in_bytes,
           },

lib/dea/stat_collector.rb

@@ -7,13 +7,15 @@ class StatCollector
     attr_reader :used_memory_in_bytes
     attr_reader :used_disk_in_bytes
     attr_reader :computed_pcpu
+    attr_reader :computed_dcpu
 
     def initialize(container, application_id, instance_index)
      @container = container
      @application_id = application_id
      @instance_index = instance_index
      @cpu_samples = []
      @computed_pcpu = 0
+     @computed_dcpu = 0
      @used_memory_in_bytes = 0
      @used_disk_in_bytes = 0
     end
@@ -48,6 +50,7 @@ def compute_cpu_usage(usage, now)
         elapsed = @cpu_samples[1][:timestamp_ns] - @cpu_samples[0][:timestamp_ns]
 
         if elapsed > 0
+          @computed_dcpu = used.to_f / elapsed
           @computed_pcpu = (used * 100).to_f / elapsed
         end
       end

spec/unit/stat_collector_spec.rb

@@ -49,6 +49,7 @@
 
   it 'initializes the statistic variables to 0' do
     expect(collector.computed_pcpu).to eq(0)
+    expect(collector.computed_dcpu).to eq(0)
     expect(collector.used_memory_in_bytes).to eq(0)
     expect(collector.used_disk_in_bytes).to eq(0)
   end
@@ -92,6 +93,7 @@
       collector.emit_metrics(Time.now())
 
       expect(collector.computed_pcpu).to eq(0)
+      expect(collector.computed_dcpu).to eq(0)
       expect(collector.used_memory_in_bytes).to eq(expected_memory_usage)
       expect(collector.used_disk_in_bytes).to eq(expected_disk_usage)
     end
@@ -164,8 +166,10 @@
 
         time_between_stats = (Dea::StatCollector::INTERVAL * NANOSECONDS_PER_SECOND)
         expected_pcpu = (10_000_000_000 - 5_000_000) * 100 / time_between_stats
+        expected_dcpu = expected_pcpu / 100.0
 
         expect(collector.computed_pcpu).to eq(expected_pcpu)
+        expect(collector.computed_dcpu).to eq(expected_dcpu)
         expect(collector.used_memory_in_bytes).to eq(1000)
         expect(collector.used_disk_in_bytes).to eq(78)
       end