performance regression when filling in a table

Hello devs,

On my SSD Ubuntu laptop, with postgres-distributed binaries and unmodified 
default settings using local connections:

   ## pg 11.2
   > time pgbench -i -s 100
   ...
   done in 31.51 s
   # (drop tables 0.00 s, create tables 0.01 s, generate 21.30 s, vacuum 3.32 s, primary keys 6.88 s).
   # real    0m31.524s

   ## pg 12devel (cd3e2746)
   > time pgbench -i -s 100
   # done in 38.68 s
   # (drop tables 0.00 s, create tables 0.02 s, generate 29.70 s, vacuum 2.92 s, primary keys 6.04 s).
   real    0m38.695s

That is an overall +20% regression, and about 40% on the generate phase 
alone. This is not a fluke, repeating the procedure shows similar results.

Is it the same for other people out there, or is it only something related 
to my setup?

What change could explain such a significant performance regression?

-- 
Fabien.