$ glxinfo | grep Mesa
client glx vendor string: Mesa Project and SGI
OpenGL renderer string: Mesa DRI Intel(R) Ironlake Mobile 
OpenGL version string: 2.1 Mesa 10.3.0-devel (git-6c2d815 trusty-oibaf-ppa)

$ DRI_PRIME=1 glxinfo | grep Mesa
client glx vendor string: Mesa Project and SGI
OpenGL core profile version string: 3.3 (Core Profile) Mesa 10.3.0-devel
(git-6c2d815 trusty-oibaf-ppa)
OpenGL version string: 3.0 Mesa 10.3.0-devel (git-6c2d815 trusty-oibaf-ppa)