By way of explanation what precompile does is reduce the julia function to an intermediate representation suitable for final binary generation. It is mainly used when building the system image, as what basically happens at the end of system image generation is that all functions in intermediate representation get collected and then collectively assembled into the final binary. In JIT operation, both steps usually happen when you call the function, though in your example precompile does the first step. The reason you don't see much of an impact of what precompile does is that your function is relatively simple so type inference and codegen don't have to work very hard as compared to the actual binary generation.
Maybe precompile in REPL mode should also do the final compilation, but I hope that explanation is at least useful. On Thu, Jun 12, 2014 at 10:47 AM, Cristóvão Duarte Sousa <cris...@gmail.com> wrote: > Hi, > > With Julia 0.3.0-prerelease+3609 (Commit 664cab5 (2014-06-10 05:18 UTC)) > in Arch Linux x86_64, > precompile() doesn't seems to effectively improve functions first call > time. > For example, this code: > > N = 10 > A = rand(N,N) > B = rand(N,N) > > > function f(a, b) > c=a+b > c > end > > > @time precompile(f, typeof((A,B))); > @time f(A,B); > @time f(A,B); > @time f(A,B); > > usually outputs something like > > elapsed time: 0.001388013 seconds (21972 bytes allocated) > elapsed time: 0.001305722 seconds (1008 bytes allocated) > elapsed time: 7.486e-6 seconds (1008 bytes allocated) > elapsed time: 7.128e-6 seconds (1008 bytes allocated) > > > Isn't precompile supposed mitigate the first call time overhead? > Am I missing something? >
