Groups   120 of 99+      julia-users › Possible bug: very slow module load after addprocs   7 posts by 2 authors      Marius Millea    Jul 19   I noticed that once I addprocs  , subsequent  using  statements were extremely slow. I guess in this case its loading the module on each processor, but if it happens in parallel it shouldn't be  that  much more wall time, and here I'm talking about two orders of magnitude difference.   Assuming I've got a file Empty-jl who contents is,  module Empty end  then single threaded:  tic   using Empty toc   elapsed time: 0.024461076 seconds  vs. multi-threaded:  addprocs    I've got 8 procs tic   using Empty toc   elapsed time: 2.479418079 seconds   Should I submit this as an Issue on Github, or is there something else going on? I've checked both Julia 0.4.5. and 0.5  01e3c8a . I'm on Ubuntu 16.04 64bit.        Cedric St-Jean    Jul 19   Maybe there is some warm-up JIT time in there? If you create an Empty2 module and load it after Empty, is it also slow?      Marius Millea    Jul 19   Seems it may have something to do with that. If I understood correctly what you're saying, if I create Empty2-jl defining module Empty2, I get,   julia  addprocs  ;  julia  tic  ; using Empty; toc   elapsed time: 2.706353202 seconds 2.706353202  julia  tic  ; using Empty; toc   elapsed time: 0.00042397 seconds 0.00042397  julia  tic  ; using Empty2; toc   elapsed time: 0.029200919 seconds 0.029200919  julia  tic  ; using Empty2; toc   elapsed time: 0.000193097 seconds 0.000193097    That first load of Empty2 at 0.02 secs is much more in line with what loading it on a single processor takes.       Cedric St-Jean    Jul 19  Re:  julia-users  Re: Possible bug: very slow module load after addprocs    Yes, that's what I meant. Presumably the multi-proc machinery is getting compiled at the first `using`. It's the same reason why  println 2+2   is very slow on first use, but fast afterwards.       Marius Millea    Jul 20  Re:  julia-users  Re: Possible bug: very slow module load after addprocs    I don't think that theory totally works, it seems to scale to some extent with the length of time to load the package itself. Another example:  julia  tic  ; using PyPlot; toc   elapsed time: 3.395904233 seconds  vs  julia  addprocs  ; julia  tic  ; using PyPlot; toc   elapsed time: 13.877550518 seconds  or even:  julia  addprocs  ; julia  using Empty; tic  ; using PyPlot; toc   elapsed time: 7.357315778 seconds   In any case, it can get pretty painful loading a few modules at the beginning of my parallelized scripts...         Cedric St-Jean    Jul 20  Re:  julia-users  Re: Possible bug: very slow module load after addprocs    That does look suspicious. Maybe file an issue if there isn't one?      Marius Millea    Jul 20  Re:  julia-users  Re: Possible bug: very slow module load after addprocs    Done, see https:  github.com JuliaLang julia issues 17509