After flashing my GPU following this documentation I still had 27.X Mh/s only.
http://1stminingrig.com/best-bios-rom-for-sapphire-rx-580-8gb-special-edition-hynix-memory-31-mhs/
Other people reported 30+ Mh/s, so I googled and found the solution to improve it. I wrote the below instructions because I didn’t find them somewhere else.
My new hashrate is 30.8 Mh/s for ETH and 887 H/s for XMR.
The culprit is that my card has actually 2x memory chips (Samsung + Hynix) and not only one as shown in GPU-Z.
Instructions
- Download SRBPolaris Bios Editor
https://bitcointalk.org/index.php?topic=1882656.0 - Download Atiflash 2.77
https://www.techpowerup.com/download/ati-atiflash/
1. Save a copy of your GPU BIOS (256kb in my case) and open it with SRBPolaris editor and you see that the GPU has 2 memory types. This can vary from vendor to vendor.
2. Now click on “Mem. Timings” tab and click the “Strap 1750 to upper” on the right. This will automatically copy the 1750 timing into the 2000 and 2250 timings on both memory chips.
3. Save the BIOS and flash it back to your GPU.
4. DONE
Now I see much better hashrates (>30 MH/s) in dual-mode with DCR and much more stable too. Still not as good as on 1stminingrig.com but acceptable.