Hi all, recently I did some micro-benchmarks of parallel code on my 8-core computer. But I don't get the point about this behaviour of pmap. Can anyone explain this to me? The code is running on a dual quad-core intel machine (Xeon X5482, 3.20 GHz).
(defn maptest [cores] (doall (map (fn [x] (dotimes [_ 1000000000] (inc 0))) (range len)))) (defn pmaptest [cores] (doall (pmap (fn [x] (dotimes [_ 1000000000] (inc 0))) (range len)))) leads to: (time (maptest 8)) : 20804.182202 msecs (time (pmaptest 8)) : 2567.521341 msecs i.e. a speedup of ~8. Doing this with doubles: (defn maptest [cores] (doall (map (fn [x] (dotimes [_ 1000000000] (inc 0.1))) (range len)))) (defn pmaptest [cores] (doall (pmap (fn [x] (dotimes [_ 1000000000] (inc 0.1))) (range len)))) leads to: (time (maptest 8)) : 68044.060324 msecs (time (pmaptest 8)) : 35051.174503 msecs i.e. a speedup of ~2. However, the CPU usage indicated by "top" is ~690%. What does the CPU do? Regards, Johann --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
