Nested servers frame rate

[Daniel van Vugt]

At first glance, comparing frame rates between direct (single) and 
nested (double) server configurations reveals nothing unexpected...

Full screen
Direct (bypass) 2600
Direct (bypass off) 2400
Nested (bypass) 2450
Nested (bypass off) 2330

But for surfaces which can't be bypassed, something strange happens; 
nesting is faster!

Windowed
Nested 4890
Direct 4400

My best theory right now is that we're crippling Mir in the single 
server case due to:
https://bugs.launchpad.net/mir/+bug/1253868
and nesting provides a workaround for that problem by supplying extra 
levels of buffering.

Can anyone else think why nested would sometimes be faster than not nested?

- Daniel