Sometimes long test-running on Apple-MAC machines may be slowed-down while Silk Mobile UI is in background. The following property in file app.properties may be useful to prevent such downgrades:
mac.disturbance=<msec>
where <msec> is an integer value in milliseconds. Its default value is 180,000, i.e., 3 minutes. You can shorten this period by assigning a smaller value. If you do not experience performance problems in running tests on Mac, you are advised to cancel this property at all by assigning it value 0.