new doc

Author: digoal

201912/20191228_04.md

@@ -288,6 +288,71 @@ if test -f /sys/kernel/mm/transparent_hugepage/enabled; then
 fi        
 ```  
 
+### 修改时钟（可选）
+```
+vi /etc/rc.local
+
+touch /var/lock/subsys/local
+
+if test -f /sys/kernel/mm/transparent_hugepage/enabled; then
+   echo never > /sys/kernel/mm/transparent_hugepage/enabled
+fi
+   
+echo tsc > /sys/devices/system/clocksource/clocksource0/current_clocksource   
+```
+  
+支持的时钟：  
+  
+```  
+cat /sys/devices/system/clocksource/clocksource0/available_clocksource   
+kvm-clock tsc acpi_pm   
+```  
+  
+修改时钟：  
+  
+```  
+echo tsc > /sys/devices/system/clocksource/clocksource0/current_clocksource   
+```  
+  
+时钟性能：  
+  
+```  
+kvm-clock:   
+  
+pg_test_timing   
+Testing timing overhead for 3 seconds.  
+Per loop time including overhead: 38.05 ns  
+Histogram of timing durations:  
+  < us   % of total      count  
+     1     96.22568   75875976  
+     2      3.76667    2970102  
+     4      0.00055        435  
+     8      0.00704       5550  
+    16      0.00005         42  
+    32      0.00000          1  
+    64      0.00000          1  
+   128      0.00000          0  
+   256      0.00000          0  
+   512      0.00000          0  
+  1024      0.00000          1  
+  
+tsc:  
+  
+pg_test_timing   
+Testing timing overhead for 3 seconds.  
+Per loop time including overhead: 31.93 ns  
+Histogram of timing durations:  
+  < us   % of total      count  
+     1     96.82838   90964258  
+     2      3.16507    2973390  
+     4      0.00078        731  
+     8      0.00574       5394  
+    16      0.00003         26  
+    32      0.00000          2  
+```  
+  
+tsc 略好  
+  
 ### 启动irqbalance服务  
 ```  
 systemctl enable irqbalance