From 664ed2a6fd2b324bb6b56db3d3eca853cfda8f61 Mon Sep 17 00:00:00 2001
From: Lukas Larsson <lukas@erlang-solutions.com>
Date: Fri, 12 Sep 2014 16:38:00 +0200
Subject: erts: Add microstate accounting

Microstate accounting is a way to track which state the
different threads within ERTS are in. The main usage area
is to pin point performance bottlenecks by checking which
states the threads are in and then from there figuring out
why and where to optimize.

Since checking whether microstate accounting is on or off is
relatively expensive if done in a short loop only a few of the
states are enabled by default and more states can be enabled
through configure.

I've done some benchmarking and the overhead with it turned off
is not noticible and with it on it is a fraction of a percent.
If you enable the extra states, depending on the benchmark,
the ovehead when turned off is about 1% and when turned on
somewhere inbetween 5-15%.

OTP-12345
---
 erts/preloaded/src/erts_internal.erl | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

(limited to 'erts/preloaded/src/erts_internal.erl')

diff --git a/erts/preloaded/src/erts_internal.erl b/erts/preloaded/src/erts_internal.erl
index c3a14d272d..a15355bb10 100644
--- a/erts/preloaded/src/erts_internal.erl
+++ b/erts/preloaded/src/erts_internal.erl
@@ -49,6 +49,9 @@
 
 -export([is_system_process/1]).
 
+-export([await_microstate_accounting_modifications/3,
+	 gather_microstate_accounting_result/2]).
+
 %% Auto import name clash
 -export([check_process_code/2]).
 
@@ -355,3 +358,28 @@ perf_counter_unit() ->
 
 is_system_process(_Pid) ->
     erlang:nif_error(undefined).
+
+-spec await_microstate_accounting_modifications(Ref, Result, Threads) -> boolean() when
+      Ref :: reference(),
+      Result :: boolean(),
+      Threads :: pos_integer().
+
+await_microstate_accounting_modifications(Ref, Result, Threads) ->
+    _ = microstate_accounting(Ref,Threads),
+    Result.
+
+-spec gather_microstate_accounting_result(Ref, Threads) -> [#{}] when
+      Ref :: reference(),
+      Threads :: pos_integer().
+
+gather_microstate_accounting_result(Ref, Threads) ->
+    microstate_accounting(Ref, Threads).
+
+microstate_accounting(_Ref, 0) ->
+    [];
+microstate_accounting(Ref, Threads) ->
+    receive
+        Ref -> microstate_accounting(Ref, Threads - 1);
+        {Ref, Res} ->
+	    [Res | microstate_accounting(Ref, Threads - 1)]
+    end.
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