Here is the solution:
The new ROCm Kernel works great, my hashrate went from 155 > 167Mhs/s with 6*RX470 with Ubuntu 16.4

#Install new ROCm Kernel:

wget -qO - http://repo.radeon.com/rocm/apt/debian/rocm.gpg.key | sudo apt-key add -
sudo sh -c 'echo deb [arch=amd64] http://repo.radeon.com/rocm/apt/debian/ xenial main > /etc/apt/sources.list.d/rocm.list'
sudo apt-get update
sudo apt-get install rocm

#edit grub
sudo nano  /etc/default/grub
#2MB fragments for Ellesmere are enabled with a grub option:
GRUB_CMDLINE_LINUX="amdgpu.vm_fragment_size=9"

sudo update-grub
sudo reboot

choose new Kernel and its done!

Thx to gstoner from ROCm Github.


Feel free to donate if you happy ;-)

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Greetz