在Linux内核启动时打印时间

  具体实现方法：make menuconfig ---> Kernel hacking --> show timing information on printks

  当选中这个选项后，启动内核，会在log信息前面加上时间信息。

  如下:

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Uncompressing Linux... done, booting the kernel.
[ 0.000000] Linux version 2.6.35.7+ (bshen@bamboo) (gcc version 4.4.1 (Sourcery G++ Lite 2010q1-202) ) #109 PREEMPT Mon Nov 14 15:11:15 CST 2011
[ 0.000000] CPU: ARM926EJ-S [41069265] revision 5 (ARMv5TEJ), cr=00053177
[ 0.000000] CPU: VIVT data cache, VIVT instruction cache

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