Improve samba and minidlna perfomance on Netgear WNDR4700

With stock firmware, I can get excellent speed when copy files from router to local drive, both with samba and minidlna( more than 70MB/s ). minidlna even reaches 110MB/s with about 10% cpu usage.
But on lede 17.01, smbd and minidlna eats up my cpu , and the download speed rarely reaches 20MB/s. What could be the cause? Did Netgear add some magic to the stock firmware?
By the way, the hard drive is ext4-formated and attached to sata port, and I am connecting to the router with gigabit ethernet

How do you test the minidlna speed?

Through windows explorer

I tried to compile and install glibc version of lede, same result.