Originally Posted by AaronP
The rotation is performed by the GPU. While there's some slowdown because the GPU is doing more work, it shouldn't be as slow as you're saying it was.
Though I reported success earlier today, I think there is actually still the problem I experienced a year ago last time I tried the Rotate option. The difference now, I think, is that I am using a dual-core processor, so I didn't notice the slowdown right away.
In particular, even just sitting with top(1) running but otherwise idle, I observe that X consumes about 7% of one of my cores. By contrast, when I run without the Rotate option, this is under 1%. To me, this suggests my CPU is doing work for the rotation that is normally performed by the GPU.
The reason I checked my CPU usage is that I noticed slowdown while performing compilation, which nearly fully-utilizes both cores. When both cores are utilized, my UI experience starts to become noticeably slower. This happens with the Rotate option, but it would never happen when rotating via RandR.
So, is this a bug in (my version of) X, or in the nvidia drivers?