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 <christophe@raffalli.eu> 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