Hi Harry,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v5.0-rc4 next-20190222]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Harry-Pan/PM-sleep-measure-the-time-of-filesystem-syncing/20190225-023616
config: nds32-defconfig (attached as .config)
compiler: nds32le-linux-gcc (GCC) 6.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=6.4.0 make.cross ARCH=nds32 

All errors (new ones prefixed by >>):

   kernel/power/main.o: In function `ksys_sync_helper':
>> main.c:(.text+0x150): undefined reference to `__moddi3'
   main.c:(.text+0x154): undefined reference to `__moddi3'
>> main.c:(.text+0x168): undefined reference to `__divdi3'
   main.c:(.text+0x16c): undefined reference to `__divdi3'

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