Nested procedures into X12

[Adam Jackson]

On Wed, 2015-06-17 at 14:05 -0700, Jasper St. Pierre wrote:

> And yet it's still fast enough. Eliminating roundtrips would be nice,
> but we should make sure we're eliminating the roundtrips that matter.

On a 2.3GHz haswell I get about 100k roundtrips per second (measuring
with x11perf -pointer).  92 round trips is 0.92 milliseconds.  That's
twice as long as the vblank interval with CVT-R timing.  So unless
you're racing the scanline and/or scheduling slow work for the top of
the frame, you have about a 2% chance that mapping a window means
missing a frame.  Maybe mutter gets that right, but I kind of doubt it
has that good of an internal cost model.

A 2.3GHz haswell is a fast, modern machine.  On a 1.7GHz ivybridge I
get about 50k/sec.  On an SGI Indy you could expect maybe 1.8k/sec; 92
round trips would be 5ms, a third of a frame.  Granted not many people
make 150MHz MIPS machines these days, but they _are_ making atoms.

- ajax