The emulator qemu-system-i386.exe cpu usage almost constantly running between 7~9
Android studio 2.1 Android SDK Tools: 25.1.3 Host Operating System: Windows 7 - i7
The cause of the constant CPU usage could be the sound. If you do not need sound in your emulator you can disable it by editing the AVD's config file.
Change/add those two lines
hw.audioInput=no
hw.audioOutput=no
Update: As buncis commented you can also try to disable GPS if not needed:
hw.GPS = no
On Linux/Mac the file is located at ~/.android/avd/
On Windows the file is located at C:\Users\