[observer] Improve measurement of CPU utilization in etop

Now using scheduler_wall_time instead of runtime/wall_clock to get cpu
utilization. The old version could give CPU utilization far beyond 100%.

Also, a bug which sometimes gave a badarith when calculating the CPU
utilization is corrected.

2 files changed, 39 insertions, 14 deletions

diff --git a/lib/runtime_tools/include/observer_backend.hrl b/lib/runtime_tools/include/observer_backend.hrl
index 4be9baca5b..91647a4468 100644
--- a/lib/runtime_tools/include/observer_backend.hrl
+++ b/lib/runtime_tools/include/observer_backend.hrl
@@ -1,26 +1,27 @@
-%% ``The contents of this file are subject to the Erlang Public License,
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2002-2013. All Rights Reserved.
+%%
+%% The contents of this file are subject to the Erlang Public License,
 %% Version 1.1, (the "License"); you may not use this file except in
 %% compliance with the License. You should have received a copy of the
 %% Erlang Public License along with this software. If not, it can be
-%% retrieved via the world wide web at http://www.erlang.org/.
-%% 
+%% retrieved online at http://www.erlang.org/.
+%%
 %% Software distributed under the License is distributed on an "AS IS"
 %% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
 %% the License for the specific language governing rights and limitations
 %% under the License.
-%% 
-%% The Initial Developer of the Original Code is Ericsson Utvecklings AB.
-%% Portions created by Ericsson are Copyright 1999, Ericsson Utvecklings
-%% AB. All Rights Reserved.''
-%% 
-%%     $Id$
+%%
+%% %CopyrightEnd%
 %%
 
 -record(etop_info, 
 	{now = {0, 0, 0},
 	 n_procs = 0,
-	 wall_clock = {0, 0},
-	 runtime = {0, 0},
+	 wall_clock,
+	 runtime,
 	 run_queue = 0,
 	 alloc_areas = [],
 	 memi = [{total, 0},
diff --git a/lib/runtime_tools/src/observer_backend.erl b/lib/runtime_tools/src/observer_backend.erl
index e8c9b50c33..d1d291d5cb 100644
--- a/lib/runtime_tools/src/observer_backend.erl
+++ b/lib/runtime_tools/src/observer_backend.erl
@@ -217,15 +217,39 @@ fetch_stats_loop(Parent, Time) ->
 %% etop backend
 %%
 etop_collect(Collector) ->
+    %% If this is the first time and the scheduler_wall_time flag is
+    %% false, SchedulerWallTime will be 'undefined' (and show 0 cpu
+    %% utilization in etop). Next time the flag will be true and then
+    %% there will be a measurement.
+    SchedulerWallTime = erlang:statistics(scheduler_wall_time),
+
+    %% Turn off the flag while collecting data per process etc.
+    case erlang:system_flag(scheduler_wall_time,false) of
+	false ->
+	    %% First time and the flag was false - start a monitoring
+	    %% process to set the flag back to false when etop is stopped.
+	    spawn(fun() -> flag_holder_proc(Collector) end);
+	_ ->
+	    ok
+    end,
+
     ProcInfo = etop_collect(processes(), []),
+
     Collector ! {self(),#etop_info{now = now(),
 				   n_procs = length(ProcInfo),
 				   run_queue = erlang:statistics(run_queue),
-				   wall_clock = erlang:statistics(wall_clock),
-				   runtime = erlang:statistics(runtime),
+				   runtime = SchedulerWallTime,
 				   memi = etop_memi(),
 				   procinfo = ProcInfo
-				  }}.
+				  }},
+    erlang:system_flag(scheduler_wall_time,true).
+
+flag_holder_proc(Collector) ->
+    Ref = erlang:monitor(process,Collector),
+    receive
+	{'DOWN',Ref,_,_,_} ->
+	    erlang:system_flag(scheduler_wall_time,false)
+    end.
 
 etop_memi() ->
     try