Try to get the weighting factor right.

3 files changed, 19 insertions, 12 deletions

diff --git a/src/rabbit_misc.erl b/src/rabbit_misc.erl
index 80e160d9..45f9751a 100644
--- a/src/rabbit_misc.erl
+++ b/src/rabbit_misc.erl
@@ -71,6 +71,7 @@
 -export([ensure_timer/4, stop_timer/2]).
 -export([get_parent/0]).
 -export([store_proc_name/1, store_proc_name/2]).
+-export([moving_average/4]).
 
 %% Horrible macro to use in guards
 -define(IS_BENIGN_EXIT(R),
@@ -251,6 +252,7 @@
 -spec(get_parent/0 :: () -> pid()).
 -spec(store_proc_name/2 :: (atom(), rabbit_types:proc_name()) -> ok).
 -spec(store_proc_name/1 :: (rabbit_types:proc_type_and_name()) -> ok).
+-spec(moving_average/4 :: (float(), float(), float(), float()) -> float()).
 -endif.
 
 %%----------------------------------------------------------------------------
@@ -1088,6 +1090,12 @@ stop_timer(State, Idx) ->
 store_proc_name(Type, ProcName) -> store_proc_name({Type, ProcName}).
 store_proc_name(TypeProcName)   -> put(process_name, TypeProcName).
 
+moving_average(_Time, _HalfLife, Next, undefined) ->
+    Next;
+moving_average(Time,  HalfLife,  Next, Current) ->
+    Weight = math:exp(Time * math:log(0.5) / HalfLife),
+    Next * (1 - Weight) + Current * Weight.
+
 %% -------------------------------------------------------------------------
 %% Begin copypasta from gen_server2.erl
 
diff --git a/src/rabbit_queue_consumers.erl b/src/rabbit_queue_consumers.erl
index bea7e0d0..c9540da8 100644
--- a/src/rabbit_queue_consumers.erl
+++ b/src/rabbit_queue_consumers.erl
@@ -27,6 +27,9 @@
 
 -define(UNSENT_MESSAGE_LIMIT,          200).
 
+%% Utilisation average calculations are all in μs.
+-define(USE_AVG_HALF_LIFE, 1000000.0).
+
 -record(state, {consumers, use}).
 
 -record(consumer, {tag, ack_required, args}).
@@ -430,11 +433,6 @@ update_use({inactive, Since, Active, Avg},   active) ->
 
 use_avg(Active, Inactive, Avg) ->
     Time = Inactive + Active,
-    Ratio = Active / Time,
-    Weight = erlang:min(1, Time / 1000000),
-    case Avg of
-        undefined -> Ratio;
-        _         -> Ratio * Weight + Avg * (1 - Weight)
-    end.
+    rabbit_misc:moving_average(Time, ?USE_AVG_HALF_LIFE, Active / Time, Avg).
 
 now_micros() -> timer:now_diff(now(), {0,0,0}).
diff --git a/src/rabbit_variable_queue.erl b/src/rabbit_variable_queue.erl
index e2d8ecc8..6df04552 100644
--- a/src/rabbit_variable_queue.erl
+++ b/src/rabbit_variable_queue.erl
@@ -383,11 +383,14 @@
                                          end_seq_id   = Z }).
 
 -define(MICROS_PER_SECOND, 1000000.0).
--define(SECONDS_FOR_RATE_AVG, 10.0).
+
+%% We're sampling every 5s for RAM duration; a half life that is of
+%% the same order of magnitude is probably about right.
+-define(RATE_AVG_HALF_LIFE, 5.0).
 
 %% We will recalculate the #rates{} every time we get asked for our
 %% RAM duration, or every N messages, whichever is sooner. We do this
-%% since the priority calcuations in rabbit_amqqueue_process need
+%% since the priority calculations in rabbit_amqqueue_process need
 %% fairly fresh rates.
 -define(MSGS_PER_RATE_CALC, 1000).
 
@@ -749,11 +752,9 @@ update_rates(State = #vqstate{ in_counter      = InCount,
                    ack_out_counter = 0,
                    rates           = Rates }.
 
-update_rate(Now, TS, Count, Rate0) ->
+update_rate(Now, TS, Count, Rate) ->
     Time = timer:now_diff(Now, TS) / ?MICROS_PER_SECOND,
-    Rate = Count / Time,
-    Weight = erlang:min(1, Time / ?SECONDS_FOR_RATE_AVG),
-    Rate * Weight + Rate0 * (1 - Weight).
+    rabbit_misc:moving_average(Time, ?RATE_AVG_HALF_LIFE, Count / Time, Rate).
 
 ram_duration(State0) ->
     State = #vqstate {