Some of us want/need both tickless and smart scheduling in the X server.
To give a bit of data: on my machine, a 1x1 rectangle can go almost 2
million rectangles/second; a 500x500 rectangle is only 2800/second. You
can see the tremendous variation (and this is on accelerated hardware;
the variation can in fact be much larger than this, if the operation has
to be done in software fall-backs).
This is why the X server needs to know the time so much, so cheaply; we
have to be able to tell how much time a given client has been using, and
it can't be computed from anything but the time; otherwise individual
clients can "starve" other clients, and interactive feel goes to pot.
- Jim