diff --git a/helper/perftool.php b/helper/perftool.php
index e0bf8d7..39a8691 100644
--- a/helper/perftool.php
+++ b/helper/perftool.php
@@ -20,13 +20,13 @@ if(!is_fn("get_cpu_idle")) {
 }
 
 if(!is_fn("set_min_cpu_idle")) {
-    function set_min_cpu_idle($idle=0.01) {
+    function set_min_cpu_idle($ratio=0.01) {
         $wait = 0;
 
         // default (cpu_sleep_time): 3 seconds
-        $cpu_sleep_time =  floatval(get_value_in_array("cpu_sleep_time", $config, 3));
-        if($idle > 0 && $idle < 1) {
-            while(get_cpu_idle() < $idle) {
+        $cpu_sleep_time = floatval(get_value_in_array("cpu_sleep_time", $config, 3));
+        if($ratio > 0 && $ratio < 1) {
+            while(get_cpu_idle() < $ratio) {
                 if($wait == 0) {
                     write_common_log("CPU usage exceeded. wait a few seconds...", "helper/preftool");
                 }
@@ -42,3 +42,15 @@ if(!is_fn("set_min_cpu_idle")) {
     }
 }
 
+if(!is_fn("set_cpu_usage_limit")) {
+    function set_cpu_usage_limit($ratio=0.9) {
+        $config = get_config();
+        $num_cores = get_value_in_array("cpu_num_cores", $config, 1);
+        $pid = get_shared_var("mypid");
+
+        if(!empty($pid) && loadHelper("exectool")) {
+            write_common_log(sprintf("CPU usage limit setted. PID=%s, LIMIT=%s", $pid, ($ratio * $num_cores) * 100), "helper/perftool");
+            exec_command(sprintf("cpulimit --pid %s --limit %s", $pid, ($ratio * $num_cores) * 100));
+        }
+    }
+}