Remove use of monotonic time in pre-18 code

This has been seen to be a bottleneck at high load: each undef results
in a loop out to the code server.

Originally implemented as suggested in the erts user's guide, in commits
e6d19a18 and d4386254.

2 files changed, 6 insertions, 35 deletions

diff --git a/lib/diameter/src/base/diameter_lib.erl b/lib/diameter/src/base/diameter_lib.erl
index 3f327f3653..6a94e32b0e 100644
--- a/lib/diameter/src/base/diameter_lib.erl
+++ b/lib/diameter/src/base/diameter_lib.erl
@@ -102,8 +102,7 @@ fmt(T) ->
 %% ---------------------------------------------------------------------------
 
 -type timestamp() :: {non_neg_integer(), 0..999999, 0..999999}.
--type now() :: integer() %% monotonic time
-             | timestamp().
+-type now() :: timestamp().
 
 -spec now()
    -> now().
@@ -112,11 +111,7 @@ fmt(T) ->
 %% otherwise.
 
 now() ->
-    try
-        erlang:monotonic_time() 
-    catch
-        error: undef -> erlang:now()
-    end.
+    erlang:now().
 
 %% ---------------------------------------------------------------------------
 %% # timestamp/1
@@ -126,15 +121,7 @@ now() ->
    -> timestamp().
 
 timestamp({_,_,_} = T) ->  %% erlang:now()
-    T;
-
-timestamp(MonoT) ->  %% monotonic time
-    MicroSecs = monotonic_to_microseconds(MonoT + erlang:time_offset()),
-    Secs = MicroSecs div 1000000,
-    {Secs div 1000000, Secs rem 1000000, MicroSecs rem 1000000}.
-
-monotonic_to_microseconds(MonoT) ->
-    erlang:convert_time_unit(MonoT, native, micro_seconds).
+    T.
 
 %% ---------------------------------------------------------------------------
 %% # now_diff/1
@@ -162,10 +149,7 @@ now_diff(Time) ->
  when MicroSecs :: non_neg_integer().
 
 micro_diff({_,_,_} = T0) ->
-    timer:now_diff(erlang:now(), T0);
-
-micro_diff(T0) ->  %% monotonic time
-    monotonic_to_microseconds(erlang:monotonic_time() - T0).
+    timer:now_diff(erlang:now(), T0).
 
 %% ---------------------------------------------------------------------------
 %% # micro_diff/2
@@ -175,12 +159,8 @@ micro_diff(T0) ->  %% monotonic time
    -> MicroSecs
  when MicroSecs :: non_neg_integer().
 
-micro_diff(T1, T0)
-  when is_integer(T1), is_integer(T0) ->  %% monotonic time
-    monotonic_to_microseconds(T1 - T0);
-
 micro_diff(T1, T0) ->  %% at least one erlang:now()
-    timer:now_diff(timestamp(T1), timestamp(T0)).
+    timer:now_diff(T1, T0).
 
 %% ---------------------------------------------------------------------------
 %% # time/1
@@ -219,15 +199,7 @@ time(Micro) ->  %% elapsed time
 
 seed() ->
     T = now(),
-    {timestamp(T), seed(T)}.
-
-%% seed/1
-
-seed({_,_,_} = T) ->
-    T;
-
-seed(T) ->  %% monotonic time
-    {erlang:phash2(node()), T, erlang:unique_integer()}.
+    {T, T}.
 
 %% ---------------------------------------------------------------------------
 %% # eval/1
diff --git a/lib/diameter/src/base/diameter_watchdog.erl b/lib/diameter/src/base/diameter_watchdog.erl
index 0607c72818..66781d7b06 100644
--- a/lib/diameter/src/base/diameter_watchdog.erl
+++ b/lib/diameter/src/base/diameter_watchdog.erl
@@ -66,7 +66,6 @@
          parent = self() :: pid(),              %% service process
          transport       :: pid() | undefined,  %% peer_fsm process
          tref :: reference()      %% reference for current watchdog timer
-               | integer()        %% monotonic time
                | tuple()          %% now()
                | undefined,
          dictionary :: module(),  %% common dictionary