You need only check the Windows Task Manager to see what application is taking up the CPU %.
Though I'm not sure if/how the Task Manager would represent the two processors.
You can right click the avast 'a' icon, select Stop on-access protection, whilst that doesn't stop the avast services there is no resident scanning enabled so there shouldn't be any increase in CPU activity related to avast scanning. When you are done with your tests, right click the avast 'a' icon, select Start on-access-protection or reboot.