With the work of Robert Ellenberg Look ahead has been greatly improved. Originally the TP could only look 1 segment ahead. This worked well for most machining operations - but large gcode programs made up of short line/arc segments run poorly. This page is comparing Linuxcnc's current TP (on segment look ahead) with the new TP (Robs work) and also some other machine controls.
The new TP allows you to set the number of segments it looks ahead. Most of the testing here had the TP set to 50 segment look ahead. Here is a great ongoing thread that shows how to test the new TP.
Couple notes. There are some design changes at this time with the new TP. -exact stops between G0 and Feed moves (and vice versa..) -In G64 - P and Q needs to be explicitly entered. (in the current TP if you don't have a Q then Q=P.)
Most testing on this page have done have been with a config setup with 500ipm and 30in/s^2.
Lets start with a simple program here.
% (1" square with 1/4"r corners) G90 G54 G20 G64 G0 X0 Y.25 Z.25 z0 G1 Y.75 F999 G2 X.25 Y1 I.25 G1 X.75 G2 X1 Y.75 J-.25 G1 Y.25 G2 X.75 Y0 I-.25 G1 X.25 G2 X0 Y.25 J.25 G0z.25 M30
This is what it looks like.
Here is the Current TP velocity plot.
Here is the New TP velocity plot.