fix(vm): cpu usage/idle handled by single worker

apps/emqx/src/emqx_cpu_sup_worker.erl

@@ -0,0 +1,91 @@
+%%--------------------------------------------------------------------
+%% Copyright (c) 2024 EMQ Technologies Co., Ltd. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%--------------------------------------------------------------------
+
+-module(emqx_cpu_sup_worker).
+
+-behaviour(gen_server).
+
+-include("logger.hrl").
+
+%% gen_server APIs
+-export([start_link/0]).
+
+-export([
+    cpu_util/0,
+    cpu_util/1
+]).
+
+%% gen_server callbacks
+-export([
+    init/1,
+    handle_continue/2,
+    handle_call/3,
+    handle_cast/2,
+    terminate/2,
+    code_change/3
+]).
+
+-define(CPU_USAGE_WORKER, ?MODULE).
+
+%%--------------------------------------------------------------------
+%% API
+%%--------------------------------------------------------------------
+
+cpu_util() ->
+    gen_server:call(?CPU_USAGE_WORKER, ?FUNCTION_NAME, infinity).
+
+cpu_util(Args) ->
+    gen_server:call(?CPU_USAGE_WORKER, {?FUNCTION_NAME, Args}, infinity).
+
+%%--------------------------------------------------------------------
+%% gen_server callbacks
+%% simply handle cpu_sup:util/0,1 called in one process
+%%--------------------------------------------------------------------
+
+start_link() ->
+    gen_server:start_link({local, ?CPU_USAGE_WORKER}, ?MODULE, [], []).
+
+init([]) ->
+    {ok, undefined, {continue, setup}}.
+
+handle_continue(setup, undefined) ->
+    %% start os_mon temporarily
+    {ok, _} = application:ensure_all_started(os_mon),
+    %% The returned value of the first call to cpu_sup:util/0 or cpu_sup:util/1 by a
+    %% process will on most systems be the CPU utilization since system boot,
+    %% but this is not guaranteed and the value should therefore be regarded as garbage.
+    %% This also applies to the first call after a restart of cpu_sup.
+    _Val = cpu_sup:util(),
+    {noreply, #{}}.
+
+handle_call(cpu_util, _From, State) ->
+    Val = cpu_sup:util(),
+    {reply, Val, State};
+handle_call({cpu_util, Args}, _From, State) ->
+    Val = erlang:apply(cpu_sup, util, Args),
+    {reply, Val, State};
+handle_call(Req, _From, State) ->
+    {reply, {error, {unexpected_call, Req}}, State}.
+
+handle_cast(Msg, State) ->
+    ?SLOG(error, #{msg => "unexpected_cast", cast => Msg}),
+    {noreply, State}.
+
+terminate(_Reason, _State) ->
+    ok.
+
+code_change(_OldVsn, State, _Extra) ->
+    {ok, State}.

apps/emqx/src/emqx_os_mon.erl

@@ -18,6 +18,7 @@
 
 -behaviour(gen_server).
 
+-include("emqx.hrl").
 -include("logger.hrl").
 
 -export([start_link/0]).
@@ -47,8 +48,6 @@
 ]).
 -export([is_os_check_supported/0]).
 
--include("emqx.hrl").
-
 -define(OS_MON, ?MODULE).
 
 start_link() ->
@@ -92,6 +91,8 @@ handle_continue(setup, undefined) ->
     SysHW = init_os_monitor(),
     MemRef = start_mem_check_timer(),
     CpuRef = start_cpu_check_timer(),
+    %% the value of the first call should be regarded as garbage.
+    _Val = cpu_sup:util(),
     {noreply, #{sysmem_high_watermark => SysHW, mem_time_ref => MemRef, cpu_time_ref => CpuRef}}.
 
 init_os_monitor() ->
@@ -131,7 +132,7 @@ handle_info({timeout, _Timer, mem_check}, #{sysmem_high_watermark := HWM} = Stat
 handle_info({timeout, _Timer, cpu_check}, State) ->
     CPUHighWatermark = emqx:get_config([sysmon, os, cpu_high_watermark]) * 100,
     CPULowWatermark = emqx:get_config([sysmon, os, cpu_low_watermark]) * 100,
-    CPUVal = emqx_vm:cpu_util(),
+    CPUVal = cpu_sup:util(),
     case CPUVal of
         %% 0 or 0.0
         Busy when Busy == 0 ->

apps/emqx/src/emqx_sys_sup.erl

@@ -28,7 +28,7 @@ start_link() ->
 init([]) ->
     OsMon =
         case emqx_os_mon:is_os_check_supported() of
-            true -> [child_spec(emqx_os_mon)];
+            true -> [child_spec(emqx_cpu_sup_worker), child_spec(emqx_os_mon)];
             false -> []
         end,
     Children =

apps/emqx/src/emqx_vm.erl

@@ -16,6 +16,8 @@
 
 -module(emqx_vm).
 
+-include("logger.hrl").
+
 -export([
     schedulers/0,
     scheduler_usage/1,
@@ -376,28 +378,29 @@ avg15() ->
     compat_windows(fun cpu_sup:avg15/0).
 
 cpu_util() ->
-    compat_windows(fun cpu_sup:util/0).
+    compat_windows(fun() -> emqx_cpu_sup_worker:cpu_util() end).
 
 cpu_util(Args) ->
-    compat_windows(fun cpu_sup:util/1, Args).
+    compat_windows(fun() -> emqx_cpu_sup_worker:cpu_util(Args) end).
 
+-spec compat_windows(function()) -> any().
+compat_windows(Fun) when is_function(Fun, 0) ->
+    case emqx_os_mon:is_os_check_supported() of
+        true ->
+            try Fun() of
+                Val when is_float(Val) -> floor(Val * 100) / 100;
+                Val when is_number(Val) -> Val;
+                Val when is_tuple(Val) -> Val;
+                _ -> 0.0
+            catch
+                _:_ -> 0.0
+            end;
+        false ->
+            0.0
+    end;
 compat_windows(Fun) ->
-    case compat_windows(Fun, []) of
-        Val when is_float(Val) -> floor(Val * 100) / 100;
-        Val when is_number(Val) -> Val;
-        _ -> 0.0
-    end.
-
-compat_windows(Fun, Args) ->
-    try
-        case emqx_os_mon:is_os_check_supported() of
-            false -> 0.0;
-            true when Args =:= [] -> Fun();
-            true -> Fun(Args)
-        end
-    catch
-        _:_ -> 0.0
-    end.
+    ?SLOG(warning, "Invalid function: ~p", [Fun]),
+    error({badarg, Fun}).
 
 load(Avg) ->
     floor((Avg / 256) * 100) / 100.

apps/emqx_management/src/emqx_mgmt.erl

@@ -205,23 +205,17 @@ cpu_stats() ->
         false ->
             [];
         true ->
-            Idle = vm_stats('cpu.idle'),
-            [
-                {cpu_idle, Idle},
-                {cpu_use, 100 - Idle}
-            ]
+            vm_stats('cpu')
     end.
 
-vm_stats('cpu.idle') ->
-    case emqx_vm:cpu_util([detailed]) of
-        {_Num, _Use, List, _} when is_list(List) -> proplists:get_value(idle, List, 0);
-        %% return {all, 0, 0, []} when cpu_sup is not started
-        _ -> 0
-    end;
-vm_stats('cpu.use') ->
-    case vm_stats('cpu.idle') of
-        0 -> 0;
-        Idle -> 100 - Idle
+vm_stats('cpu') ->
+    CpuUtilArg = [],
+    case emqx_vm:cpu_util([CpuUtilArg]) of
+        %% return 0.0 when `emqx_cpu_sup_worker` is not started
+        {all, Use, Idle, _} ->
+            [{cpu_use, Use}, {cpu_idle, Idle}];
+        _ ->
+            [{cpu_use, 0}, {cpu_idle, 0}]
     end;
 vm_stats('total.memory') ->
     {_, MemTotal} = get_sys_memory(),