poor performace of DRM/GBM

[cmarty]

I've tested the 3DPrimitives example. On the RPI3B+ with broadcom(legacy) driver I got 60fps for 1920x1080.
But when using kms driver with this ofxRpi4Window (EGL/GBM) on RPI4B o got only 10fps. Do you know what is behind that big penalty?
But when I compile OF to use default GLFW then in X I get 60fps...