benchmark record vs object

jbuild

(executable
  ((name truc)
   (libraries (benchmark))
   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -color always))
   (ocamlopt_flags (:standard -O3 -bin-annot
                    -unbox-closures -unbox-closures-factor 20))
  ))

truc.ml

let n_iter = 1_000_000

let obj = object
  method do_it n = Sys.opaque_identity (n+42)
end

let f_obj obj x =
  for _i = 1 to n_iter do
    ignore (Sys.opaque_identity (obj#do_it x))
  done

type r = {
  do_it : int -> int;
}

let r = {
  do_it = (fun n -> n+42);
}

let f_rec r x =
  for _i = 1 to n_iter do
    ignore (Sys.opaque_identity (r.do_it x))
  done

let ()=
  Benchmark.tabulate @@
  Benchmark.throughputN 3 [
    "obj", (f_obj obj), 10;
    "rec", (f_rec r), 10;
  ]