Sorry, you actually said as much "On the same examples, same options *(flambda everywhere)*," Though, the expectation that was thwarted for me is that there's no specific multicore flambda switch. Just multicore. And that 20-25% speedup felt like a familiar we-switched-to-flambda speedup to me. On Fri, Oct 8, 2021 at 5:58 PM Michael Bacarella < michael.bacarella@gmail.com> wrote: > My gut here says you're unwittingly comparing regular ocaml to flambda > ocaml. > > https://ocaml.org/manual/flambda.html > > Perhaps multicore only comes in flambda flavor now (I notice it's not > available as a switch). > > On Fri, Oct 8, 2021 at 5:07 PM Christophe Raffalli > wrote: > >> >> Hello, >> >> I managed to install ocaml 4.12.0 with multicore. I could not parallelise >> my >> code in 5mn ;-) but I check just the sequential speed and got a bit >> surprised. On the same examples, same options (flambda everywhere), etc >> ... >> >> Ex 1 Ex 2 Ex 3 >> 4.13.1 normal 45s 12s 49s >> 4.12.0 normal 36s 11s 45s >> 4.12.0 multicore 31s 10s 40s >> >> These are not small differences and it is rather surprising that >> >> 4.13.1 is significantly slower than 4.12.0 (20 to 25%) >> >> 4.12.0 + multicore is faster on sequential code. >> >> Other people observe the same ? >> Any idea ? Should I report an issue for the speed degradation of 4.13.1 ? >> >> Christophe >> >