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Forked from stolen/timetop.erl
Created January 18, 2018 16:10
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top processes by scheduled time
-module(timetop).
-export([top/2]).
top(Duration, Count) ->
OldPrio = erlang:process_flag(priority, high),
Result = scheduled_time_top(Duration),
erlang:process_flag(priority, OldPrio),
lists:sublist(Result, Count).
%% Build process top according to scheduled time
%% For simplicity, we ignore newly started processes
scheduled_time_top(Duration) when is_integer(Duration) ->
% Start collecting trace data and remember when we did that
erlang:trace(existing, true, [running,monotonic_timestamp]),
StartTime = erlang:monotonic_time(nano_seconds),
% Remember intermediate process states so we can guess if process was running all the time
Pids = erlang:processes(),
DefaultStates = [{P, S} || P <- Pids, P =/= self(), {status, S} <- [process_info(P, status)]],
% Set trace finish timer
TRef = erlang:start_timer(Duration, self(), stop_tracing),
% Collect events until timer fires
RevEvents0 = acc_sched_trace_events(StartTime, undefined, TRef, []),
% Finish tracing, remember the time
EndTime = erlang:monotonic_time(nano_seconds),
erlang:trace(existing, false, [running,monotonic_timestamp]),
% Collect remaining events
FinTRef = erlang:start_timer(50, self(), stop_collecting),
RevEvents1 = acc_sched_trace_events(StartTime, EndTime, FinTRef, []),
% Concatenate all events and put them in order
AllEvents = lists:reverse(RevEvents0, lists:reverse(RevEvents1)),
% For every traced process, calculate its runnint time percentage
RunPercentages = [{P, running_time_percentage(P, AllEvents, StartTime, EndTime, DefState)} || {P, DefState} <- DefaultStates, erlang:is_process_alive(P)],
% Sort the result
SortedRunPercentages = lists:sort(fun({_, P1}, {_, P2}) -> P1 >= P2 end, RunPercentages),
% Trim percentages for short printing by default
TrimmedSortedRunPercentages = [{P, round(R * 100) / 100} || {P, R} <- SortedRunPercentages],
% Drop any extra trace messages
drop_sched_trace_events(),
TrimmedSortedRunPercentages.
running_time_percentage(Pid, AllEvents, StartTime, EndTime, DefState) ->
PidEvents = [{Timestamp, Ev} || {Timestamp, EvPid, Ev} <- AllEvents, EvPid == Pid, StartTime =< Timestamp, Timestamp =< EndTime],
case PidEvents of
[] when DefState == running ->
100.0;
[] ->
0.0;
Events ->
caclculate_running_time(StartTime, EndTime, lists:sort(Events)) * 100.0 / (EndTime - StartTime)
end.
acc_sched_trace_events(StartTime, EndTime, TRef, Acc) ->
Self = self(),
receive
{timeout, TRef, _} ->
Acc;
{trace_ts, Pid, Ev, _, Timestamp} when Pid /= Self, StartTime =< Timestamp, (EndTime == undefined orelse Timestamp =< EndTime) ->
acc_sched_trace_events(StartTime, EndTime, TRef, [{Timestamp, Pid, Ev}|Acc]);
{trace_ts, _, _, _, _} ->
acc_sched_trace_events(StartTime, EndTime, TRef, Acc)
end.
drop_sched_trace_events() ->
receive
{trace_ts, _, _, _, _} -> drop_sched_trace_events()
after 0 -> ok
end.
caclculate_running_time(_StartTime, _EndTime, []) ->
0;
caclculate_running_time(_StartTime, EndTime, [{SingleInTime, in}]) ->
EndTime - SingleInTime;
caclculate_running_time(StartTime, EndTime, [{OutTime, out} | Events]) ->
% If we see a process out, assume it was initially in
caclculate_running_time(StartTime, EndTime, [{StartTime, in}, {OutTime, out} | Events]);
caclculate_running_time(_StartTime, EndTime, [{InTime, in}, {OutTime, out} | Events]) ->
(OutTime - InTime) + caclculate_running_time(OutTime, EndTime, Events).
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