HEVC played in HW on one core instead of SW in 4 core

hi.

I have a raspberry pi 2 which allows me to play 720p x265 in libreelec with kodi v17. It uses the 4 cores and ff-hevc-mmal (SW) so software decoding. The playback is ok

But I would preffer to use archlinux arm on my rpi2. But with kodi 17.1 it uses ff-hevc-mmal (HW) so hardware decoding and only one core at 100%. And the playback is not good. with sound skipping sometimes slow framerate and so on.

I have tried disableswmultithreading =false in advancedsettings.xml or usehevccodec = 0 and it changed nothing. I wonder why those settings changed nothing…

How can I force software rendering on 4 cores of h265 video ?

Is it a compile time flag ? a running time config ?