(defn foo [a b] (* a b)) ; <- 2 ms per 10K
(foo 3 8) ; <- 24

(defn bar [a b] (* @a @b)) ; <- 3.5 ms per 10K

(defn aref? [x] (isa? (class x) clojure.lang.ARef))
(defn foo [a b] (let [a (if (aref? a) @a a)
                      b (if (aref? b) @b b)]
                  (* a b))
(def x (ref 3))
(def y (ref 8))
(foo 3 8); <- 120 ms per 10K
(foo 3 y); <- 71 ms per 10K
(foo x 8); <- 73 ms per 10K
(foo x y); <- 6 ms per 10K

(defn aref? [x]
  (instance? clojure.lang.ARef x))

(defn foo [a b] (let [a (if (aref? a) @a a)
                      b (if (aref? b) @b b)]
                  (* a b)))
(def a (ref 3))
(def b (ref 8))
(time (dotimes [i 10000] (foo a b))) ; ~ 9ms
(time (dotimes [i 10000] (foo a 8))) ; ~ 2.7ms
(time (dotimes [i 10000] (foo 3 b))) ; ~ 2.7ms
(time (dotimes [i 10000] (foo 3 8))) ; ~ 1.7ms