No, it's not the context switching, changing isArray (a native method) to getAnnotations (a normal jvm method) gives the same time for both the parallel and serial version.
Cameron. On Saturday, December 29, 2012 10:34:42 AM UTC+11, Leonardo Borges wrote: > > In that case isn't context switching dominating your test? > > .isArray isn't expensive enough to warrant the use of pmap > > Leonardo Borges > www.leonardoborges.com > On Dec 29, 2012 10:29 AM, "cameron" <cdo...@gmail.com <javascript:>> > wrote: > >> Hi Lee, >> I've done some more digging and seem to have found the root of the >> problem, >> it seems that java native methods are much slower when called in parallel. >> The following code illustrates the problem: >> >> (letfn [(time-native [f] >> (let [c (class [])] >> (time (dorun (f >> (fn [_] (.isArray c)) >> (range 10000000))))))] >> (println "Sequential Test:") >> (time-native map) >> (println "Parallel Test:") >> (time-native pmap)) >> >> On a dual quad-core xeon box I get the following results: >> Sequential Test: >> "Elapsed time: 1054.807725 msecs" >> Parallel Test: >> "Elapsed time: 15302.605697 msecs" >> >> ie. the code executed in parallel was 15 times slower than the sequential >> version. >> The same can be seen with isInstance and isArray members of >> java.lang.Class. >> >> I'm not sure where to go from here, these functions are frequently used >> by clojure.core >> Perhaps someone with more JVM implementation knowledge can help? >> >> Cameron. >> >> -- >> You received this message because you are subscribed to the Google >> Groups "Clojure" group. >> To post to this group, send email to clo...@googlegroups.com<javascript:> >> Note that posts from new members are moderated - please be patient with >> your first post. >> To unsubscribe from this group, send email to >> clojure+u...@googlegroups.com <javascript:> >> For more options, visit this group at >> http://groups.google.com/group/clojure?hl=en > > -- 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
