Hello all!
After reading this article:
Clojure performance tips
http://gnuvince.wordpress.com/2009/05/11/clojure-performance-tips/
I wrote a macro to better compare different timings of functions and
expressions:
(defmacro time-ms [n expr]
`(let [start# (. System (nanoTime))]
(dotimes [i# ~n]
~expr)
(/ (double (- (. System (nanoTime)) start#)) 1000000.0)))
(defmacro timings [n & expr]
(let [expr-are-not-equal (cons 'not= expr)
expr-times (cons 'vector (map #(list 'time-ms n %) expr))]
`(if ~expr-are-not-equal
(do (println "Expressions:\n")
(dorun (map prn '~expr))
(println "\nare NOT equal!"))
(let [~'ts ~expr-times
~'max-time (apply max ~'ts)]
(dorun (map (fn [~'t ~'e] (printf "%8.2f ms %6.1f%% %5.1fx "
~'t (* 100.0 (/ ~'t ~'max-time)) (/ ~'max-time ~'t))
(prn ~'e))
~'ts '~expr))))))
Here are the examples:
(timings 1e6 (+ 2 4 5) (+ 2 (+ 4 5)))
787.96 ms 100.0% 1.0x (+ 2 4 5)
360.94 ms 45.8% 2.2x (+ 2 (+ 4 5))
;;;
(timings 1
(dotimes [i 1e6] (= i i))
(dotimes [i 1e6] (== i i)))
444.39 ms 100.0% 1.0x (dotimes [i 1000000.0] (= i i))
237.29 ms 53.4% 1.9x (dotimes [i 1000000.0] (== i i))
(timings 1
(dotimes [i 1e6] (= i 10))
(dotimes [i 1e6] (== i 10)))
368.37 ms 100.0% 1.0x (dotimes [i 1000000.0] (= i 10))
324.65 ms 88.1% 1.1x (dotimes [i 1000000.0] (== i 10))
;;;
(let [v [1 2 3]]
(timings 1e6
(let [[a b c] v] a b c)
(let [a (v 0) b (v 1) c (v 2)] a b c)))
920.15 ms 100.0% 1.0x (let [[a b c] v] a b c)
486.82 ms 52.9% 1.9x (let [a (v 0) b (v 1) c (v 2)] a b c)
;;;
(def v 3)
(let [l 3]
(timings 1e6 v l))
172.42 ms 100.0% 1.0x v
118.20 ms 68.6% 1.5x l
;;;
(defn len [x] (.length x))
(defn len2 [#^String x] (.length x))
(def s "abcdef")
(timings 1e5 (len s) (len2 s))
1655.12 ms 100.0% 1.0x (len s)
32.82 ms 2.0% 50.4x (len2 s)
Interesting is that the speed difference is smaller than in the
article.
Bug reports and suggestions are welcome!
Frantisek
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