Thanks to an XDA user, it is now possible to overclock the HTC One M9 easily. All you have to do is flash the XDA custom kernel for HTC One M9 and you will gain the ability to run your Android phone in three modes: Performance, Balance and Stock.
The only that you require before flashing the custom kernel is TWRP for HTC One M9 or any other custom recovery. After you have it on your phone, simply flash the custom kernel by going into recovery mode. Here are its salient features:
Easy installation with AROMA installer
latest CAF updates
optimized for performance and battery life
Performance modes: Performance, balance, and stock
USB fast charge (optional)
Backlight dimmer (optional)
Advanced Color Control
Disable fsync (optional)
Disable cover (optional)
i/o schedulers: SIO, FIOPS, BFQ, CFQ, noop, deadline, ROW
NTFS r/w support.