I'm not really an expert when it comes to the technical aspects of my graphics card.
This is basically my setup:
Windows 7 Ultimate 64-bit SP1
Intel Core i5 6600K @ 3.50GHz 33 °C
Skylake 14nm Technology
8.00GB Dual-Channel Unknown @ 1069MHz (15-15-15-35)
MSI Z170A GAMING M7 (MS-7976) (U3E1) 39 °C
ASUS VC239 (1920x1080@60Hz)
8192MB ATI AMD Radeon R9 390 Series (Sapphire/PCPartner) 45 °C
I had experienced the issue when I upgraded my software/driver version as it always pop up (I assume to have the latest drivers in case there are bug fixes)
To my surprise, from a 120fps game for Dota 2, CSGO and NBA 2K16. I now experience a 30-50FPS rate for all games. I didn't do any except for the version update. This makes me disappoint in fact that my graphics is Sapphire R9 390 8GB 512mb.
I've tried rolling back to my stock software (the cd that comes with the graphics card), it went smooth for awhile but after a day and I played again the issue came back.
I bought this setup 5mos ago and it was perfectly running fine until these updates came.
Navigate to Radeon Settings > Gaming > Global Settings and disable Power Efficiency.