The times for Julia code in my previous email are wrong, I wanted to write: 0.000126 seconds 0.004695 seconds (99.49 k allocations: 1.518 MB) 0.000871 seconds
On Sun, Nov 8, 2015 at 10:19 PM Cristóvão Duarte Sousa <cris...@gmail.com> wrote: > I agree, in fact my knowledge about branch prediction mechanisms is rather > limited. > But doing *if(rand()%2)* instead of *if(i%i)* yields times close to the > given one. On the other hand, with a single type (with *if(true)*) the > times drop to around 320 μs. > > For julia code, randomness seems to have higher impact: > 0.000103 seconds > 0.002179 seconds > 0.000915 seconds > (again, these times highly variable) > > Anyway, I updated the codes to choose the type randomly. > > On Sun, Nov 8, 2015 at 3:44 AM Stefan Karpinski <ste...@karpinski.org> > wrote: > >> Yeah, that's a good point. >> >> On Saturday, November 7, 2015, Gustavo Goretkin < >> gustavo.goret...@gmail.com> wrote: >> >>> I think branch predictors on many platforms today use a table indexed on >>> the history of the last couple of branches, so the period-two cycle you >>> have is likely getting a lot of correct branch hits. If you mean to totally >>> defeat the branch prediction, I think you should use something >>> pseudorandom. >>> On Nov 6, 2015 12:27 PM, "Cristóvão Duarte Sousa" <cris...@gmail.com> >>> wrote: >>> >>>> Hi, >>>> >>>> I've been wondering how Julia dispatching system would compare to the >>>> C++ virtual functions dispatch one. >>>> Hence, I write a simple test in both Julia and C++ that measures the >>>> calling of a function over the elements of both an array of concrete >>>> objects and another of abstract pointers to objects of derived types. >>>> >>>> Here is the code https://gist.github.com/cdsousa/f5d669fe3fba7cf848d8 . >>>> >>>> The usual timings for C++ in my machine, for the concrete and the >>>> abstract arrays respectively, are around >>>> 0.000143 seconds >>>> 0.000725 seconds >>>> >>>> For the Julia code the timings have much more variability, but they are >>>> around >>>> 0.000133 seconds >>>> 0.002414 seconds >>>> >>>> This shows that Julia (single) dispatch performance is not that bad >>>> while it has some room to improvement. >>>> >>>> If I'm doing something terribly wrong in these tests, please tell me :) >>>> >>>> PS: Thank you all, developers of Julia! >>>> >>>> >>>>
