diff options
Diffstat (limited to 'erts/doc')
| -rw-r--r-- | erts/doc/src/erlang.xml | 52 |
1 files changed, 45 insertions, 7 deletions
diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml index fbe7b36163..ed79109bdd 100644 --- a/erts/doc/src/erlang.xml +++ b/erts/doc/src/erlang.xml @@ -4935,17 +4935,51 @@ true</pre> </item> <tag><marker id="statistics_scheduler_wall_time"><c>scheduler_wall_time</c></marker></tag> <item> - <p>Returns - <c>[{Scheduler_Id, Scheduler_Worked_Time, Scheduler_Total_Time}]</c>, time lapses are since the - the system flag <seealso marker="#system_flag_scheduler_wall_time">scheduler_wall_time</seealso> - was set to true. + <p>Returns a list of tuples with + <c>{SchedulerId, ActiveTime, TotalTime}]</c>, where <c>SchedulerId</c> is an integer id of the scheduler, <c>ActiveTime</c> is + the duration the scheduler has been busy. <c>TotalTime</c> is the total time duration since + <seealso marker="#system_flag_scheduler_wall_time">scheduler_wall_time</seealso> activation. The time unit is not defined and may be subject to change. <c>scheduler_wall_time</c> should only be used to calculate relative values for scheduler-utilization. <c>ActiveTime</c> can never exceed <c>TotalTime</c>. + </p> + + <p>The definition of a busy scheduler is when it is not idle or not scheduling (selecting) a process or port, meaning; executing process code, executing linked-in-driver or NIF code, garbage collecting or handling any other memory management. + </p> + + <p> Returns <c>undefined</c> if the system flag <seealso marker="#system_flag_scheduler_wall_time"> - scheduler_wall_time</seealso> is set to false. + scheduler_wall_time</seealso> is turned off. </p> + <p>The list of scheduler information is unsorted and may come in different order - between calls. The time unit is undefined and may be changed and should only be used - to calculate relative utilization. + between calls. </p> + <p>Using <c>scheduler_wall_time</c> to calculate scheduler utilization.</p> +<pre> +> <input>erlang:system_flag(scheduler_wall_time, true).</input> +false +> <input>Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input> +ok +</pre> + <p>Some time later we will take another snapshot and calculate scheduler-utilization per scheduler.</p> +<pre> +> <input>Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input> +ok +> <input>lists:map(fun({{I, W0, T0}, {I, W1, T1}}) -> {I, (W1 - W0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)).</input> +[{1,0.9743474730177548}, + {2,0.9744843782751444}, + {3,0.9995902361669045}, + {4,0.9738012596572161}, + {5,0.9717956667018103}, + {6,0.9739235846420741}, + {7,0.973237033077876}, + {8,0.9741297293248656}] +</pre> + <p>Using the same snapshot to calculate a total scheduler-utilization.</p> +<pre> +> <input>{W, T} = lists:foldl(fun({{_, W0, T0}, {_, W1, T1}}, {Wi,Ti}) -> + {Wi + (W1 - W0), Ti + (T1 - T0)} end, {0,0}, lists:zip(Ts0,Ts1)), W/T.</input> +0.9769136803764825 +</pre> + </item> <tag><c>wall_clock</c></tag> @@ -4965,6 +4999,10 @@ true</pre> {2046,11} > <input>statistics(garbage_collection).</input> {85,23961,0}</pre> + <note> + <p><c>scheduler_wall_time</c> is by default disabled. Use <c>erlang:system_flag(scheduler_wall_time, true)</c> to enable it. </p> + </note> + </desc> </func> <func> |