"...measuring CPU usage at the subroutine level rather than at the overall service level. However, if this 0.005% regression originates from a single subroutine

"...measuring CPU usage at the subroutine level rather than at the overall service level. However, if this 0.005% regression originates from a single subroutine that consumes 0.1% of the total CPU, the relative change at the subroutine level is 0.005% / 0.1% = 5%, which is much more substantial. Consequently, small regressions are easier to detect at the subroutine level."