[Nouveau] glmark2: high CPU usage - DRI3 & modeset

[poma]

$ glmark2
=======================================================
    glmark2 2014.03
=======================================================
    OpenGL Information
    GL_VENDOR:     nouveau
    GL_RENDERER:   Gallium 0.4 on NV98
    GL_VERSION:    3.0 Mesa 11.2.0
=======================================================


/etc/X11/xorg.conf.d/nouveau.conf 
Section "Device"
  Identifier  "gpu0"
  Driver      "nouveau"
EndSection

$ ps -C glmark2 -o cmd,pcpu
CMD                         %CPU
glmark2                     16.2

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/etc/X11/xorg.conf.d/nouveau.conf 
Section "Device"
  Identifier  "gpu0"
  Driver      "nouveau"
  Option      "DRI" "3"
EndSection

$ ps -C glmark2 -o cmd,pcpu
CMD                         %CPU
glmark2                     86.4

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/etc/X11/xorg.conf.d/modeset.conf 
Section "Device"
  Identifier  "gpu0"
  Driver      "modesetting"
EndSection

$ ps -C glmark2 -o cmd,pcpu
CMD                         %CPU
glmark2                     94.5