Linux Kernel优化--关闭串口打印

使用如下patch，关闭串口打印，可以至少节省几百ms的时间。

diff --git a/arch/arm64/configs/xxx_defconfig b/arch/arm64/configs/xxx_defconfig
index c8036df..81275fa 100755
--- a/arch/arm64/configs/xxx_defconfig
+++ b/arch/arm64/configs/xxx_defconfig
@@ -2985,6 +2985,7 @@ CONFIG_PRINTK_TIME=y
 CONFIG_MESSAGE_LOGLEVEL_DEFAULT=4
 # CONFIG_BOOT_PRINTK_DELAY is not set
 # CONFIG_DYNAMIC_DEBUG is not set
+CONFIG_PRINTK_NOT_OUTPUT=y
 
 #
 # Compile-time checks and compiler options
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 98ee2a3..e997ad7 100755
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1568,7 +1568,7 @@ static void call_console_drivers(int level,
 
     if (!console_drivers)
         return;
-
+#ifdef CONFIG_PRINTK_NOT_OUTPUT
     for_each_console(con) {
         if (exclusive_console && con != exclusive_console)
             continue;
@@ -1584,6 +1584,7 @@ static void call_console_drivers(int level,
         else
             con->write(con, text, len);
     }
+#endif
 }