Stabilize call_with_huge_message_queue/1

Time measurements are always tricky, particulary on virtual hosts.
On one particular virtual host, the measured times were often 0.

Measuring the time for 100 calls instead of 10 calls helps, but
0 can still be returned, so we will also need to discard
measurements that return 0 and try again.

1 files changed, 35 insertions, 20 deletions

diff --git a/erts/emulator/test/receive_SUITE.erl b/erts/emulator/test/receive_SUITE.erl
index 83653a7a36..c7d5a3f5a0 100644
--- a/erts/emulator/test/receive_SUITE.erl
+++ b/erts/emulator/test/receive_SUITE.erl
@@ -39,25 +39,43 @@ groups() ->
 
 call_with_huge_message_queue(Config) when is_list(Config) ->
     Pid = spawn_link(fun echo_loop/0),
-
-    {Time,ok} = tc(fun() -> calls(10, Pid) end),
-
-    [self() ! {msg,N} || N <- lists:seq(1, 500000)],
+    _WarmUpTime = time_calls(Pid),
+    Time = time_calls(Pid),
+    _ = [self() ! {msg,N} || N <- lists:seq(1, 500000)],
+    io:format("Time for empty message queue: ~p", [Time]),
     erlang:garbage_collect(),
-    {NewTime1,ok} = tc(fun() -> calls(10, Pid) end),
-    {NewTime2,ok} = tc(fun() -> calls(10, Pid) end),
+    call_with_huge_message_queue_1(Pid, Time, 5).
+
+call_with_huge_message_queue_1(_Pid, _Time, 0) ->
+    ct:fail(bad_ratio);
+call_with_huge_message_queue_1(Pid, Time, NumTries) ->
+    HugeTime = time_calls(Pid),
+    io:format("Time for huge message queue: ~p", [HugeTime]),
+
+    case (HugeTime+1) / (Time+1) of
+        Q when Q < 10 ->
+            ok;
+        Q ->
+            io:format("Too high ratio: ~p\n", [Q]),
+            call_with_huge_message_queue_1(Pid, Time, NumTries-1)
+    end.
 
-    io:format("Time for empty message queue: ~p", [Time]),
-    io:format("Time1 for huge message queue: ~p", [NewTime1]),
-    io:format("Time2 for huge message queue: ~p", [NewTime2]),
-
-    case hd(lists:sort([(NewTime1+1) / (Time+1), (NewTime2+1) / (Time+1)])) of
-	Q when Q < 10 ->
-	    ok;
-	Q ->
-	    ct:fail("Best Q = ~p", [Q])
-    end,
-    ok.
+%% Time a number calls. Try to avoid returning a zero time.
+time_calls(Pid) ->
+    time_calls(Pid, 10).
+
+time_calls(_Pid, 0) ->
+    0;
+time_calls(Pid, NumTries) ->
+    case timer:tc(fun() -> calls(Pid) end) of
+        {0,ok} ->
+            time_calls(Pid, NumTries-1);
+        {Time,ok} ->
+            Time
+    end.
+
+calls(Pid) ->
+    calls(100, Pid).
 
 calls(0, _) -> ok;
 calls(N, Pid) ->
@@ -108,6 +126,3 @@ echo_loop() ->
 	    Pid ! {Ref,Msg},
 	    echo_loop()
     end.
-
-tc(Fun) ->
-    timer:tc(erlang, apply, [Fun,[]]).