40% of speed since upgrading to 4.19

[Stefan Priebe - Profihost AG <s.priebe@xxxxxxxxxxxx>]

Hello list,

while running ceph on top of bcache i was using kernel 4.12 + a bunch of
bcache related fixed.

This gave me 50 iop/s for ceph bench test (4MB sequential writes) in
writeback mode setting sequential_cutoff to 1MB.

After upgrading to 4.19.32 in a test cluster i'm only getting 16-20
iop/s for the same test.

Has any significant changed in bcache? Any new tuning needed?

Greets,
Stefan