You just have to launch a game like this:
$ GALLIUM_HUD="fps;requested-VRAM+requested-GTT" /usr/local/games/etqw/etqw
This will launch "Enemy Territory: QUAKE Wars" and displaying the FPS and the VRAM usage.
Note that ETQW have already a FPS counter embedded.
But you can use it for Steam games too:
$ GALLIUM_HUD="fps;requested-VRAM+requested-GTT" steam
Note that unfortunatly the VRAM usage is not supported on nouveau (tested with nv50 on a GeForce 210).
Maybe somebody can develop something that saves the FPS from the HUD and import them to PTS so that PTS can benchmarks any commercial game?