I have upgraded Android Studio to 3.1.2. When starting any Android Emulator (i.e. qemu-system-i386.exe), my CPU usage reaches 100%.
Update (5/1/2018): Actually everything in Android Studio is SLOW after upgrade and I did not change anything in my project (i.e. same settings, same code, same libraries). Performance was NOT a problem before upgrade.
As per Task Manager, the issue seems to be caused by the antivirus processes (McAfee):