On 23-08-2010, Ethan Burns <burns.et...@gmail.com> wrote: > On Mon, Aug 23, 2010 at 8:06 AM, Christophe TROESTLER ><christophe.troestler+oc...@umh.ac.be> wrote: >> On Thu, 19 Aug 2010 07:52:33 -0400, Ethan Burns wrote: >>> >>> let r = ref 0.0 ;; >>> for i = 0 to 1000000000 do r := float i done; >>> Printf.printf "%f\n" !r; >>> Printf.printf "words: %f\n" (Gc.stat ()).Gc.minor_words >> >> To add a precision to others' answers : float refs are unboxed >> _locally_. If you rewrite your code as >> >> let r = ref 0.0 in >> for i = 0 to 1000_000_000 do r := float i done; >> Printf.printf "%f\n" !r; >> Printf.printf "words: %f\n" (Gc.stat ()).Gc.minor_words >> >> then it runs at about the same speed as you other version. > > > $ time ./a.out > 1000000000.000000 > words: 2000000367.000000 > > real 0m2.655s > > It does seem to run a lot faster than my first version, but it also > seems to allocate a whole lot. If it is still allocating just as much > why is this version so much faster? >
Allocation on the minor heap is very cheap compared to assignement into the major heap. It is better to allocate a lot on the minor heap than to do operations on the major heap. I think the main reason for the difference is that the first example (float ref not local) implies a call to "caml_modify" (byterun/memory.c|h) which has a cost. This cost is bigger on amd64 architecture because one test is quite expensive (Is_in_heap I think) due to address space randomization. Regards, Sylvain Le Gall _______________________________________________ Caml-list mailing list. Subscription management: http://yquem.inria.fr/cgi-bin/mailman/listinfo/caml-list Archives: http://caml.inria.fr Beginner's list: http://groups.yahoo.com/group/ocaml_beginners Bug reports: http://caml.inria.fr/bin/caml-bugs
