(defclass counter ()
  ((value :initform 0 :accessor counter-value)))

(defgeneric m-inc (counter)
  (:method ((counter counter))
    (incf (counter-value counter))))

(defun f-inc (counter)
  (incf (counter-value counter)))

(defstruct s-counter
  (value 0))

(defun s-inc (counter)
  (incf (s-counter-value counter)))

(time (loop :with c := (make-instance 'counter)
            :repeat 1000000
            :do (m-inc c)
            :finally (return (counter-value c))))

(time (loop :with c := (make-instance 'counter)
            :repeat 1000000
            :do (f-inc c)
            :finally (return (counter-value c))))

(time (loop :with c := (make-s-counter)
            :repeat 1000000
            :do (s-inc c)
            :finally (return (s-counter-value c))))

(time (loop :with c := 0
            :repeat 1000000
            :do (incf c)
            :finally (return c)))

;; cl-user> (load #P"~/b.lisp")
;; (loop :with c := (make-instance 'counter) :repeat 1000000 :do (m-inc c) :finally (return (counter-value c)))
;; took 106,743 microseconds (0.106743 seconds) to run.
;; During that period, and with 8 available CPU cores,
;;       92,589 microseconds (0.092589 seconds) were spent in user mode
;;          628 microseconds (0.000628 seconds) were spent in system mode
;;  1,184 bytes of memory allocated.
;; (loop :with c := (make-instance 'counter) :repeat 1000000 :do (f-inc c) :finally (return (counter-value c)))
;; took 88,853 microseconds (0.088853 seconds) to run.
;; During that period, and with 8 available CPU cores,
;;      87,517 microseconds (0.087517 seconds) were spent in user mode
;;         824 microseconds (0.000824 seconds) were spent in system mode
;;  64 bytes of memory allocated.
;; (loop :with c := (make-s-counter) :repeat 1000000 :do (s-inc c) :finally (return (s-counter-value c)))
;; took 342,449 microseconds (0.342449 seconds) to run.
;; During that period, and with 8 available CPU cores,
;;      310,990 microseconds (0.310990 seconds) were spent in user mode
;;        3,603 microseconds (0.003603 seconds) were spent in system mode
;;  32 bytes of memory allocated.
;; (loop :with c := 0 :repeat 1000000 :do (incf c) :finally (return c))
;; took 28,144 microseconds (0.028144 seconds) to run.
;; During that period, and with 8 available CPU cores,
;;      27,932 microseconds (0.027932 seconds) were spent in user mode
;;          74 microseconds (0.000074 seconds) were spent in system mode
;; #P"/Users/pjb/b.lisp"