Question on glxGears!

[Siva]

Hi,
I know that GlxGears is not a benchmark, but I'm need to validate the
performance of a graphics driver that I'm currently working on.

What does Glxgears test exactly, when it reports fps? XServer graphics
pipeline or the graphics engine capability to handle commands?
I mean if there is a drop of 100fps, is it an indication of
significant performance drop?

Any information, pointers will be helpful.

Thanks.