Dual displays, full screenmode


I noticed that that in SDL2.0 I can create 2 or multiple windows and place
them into different positions to achieve a ‘fake’ dual display program. But,
if it is in windowed mode, I always see lags/jitters in my SDL Opengl
program, even when my program only makes a basic triangle rotate. Like the
example code in this link.

However, I remembered that in SDL1.2, if a SDL program runs in a window mode
with OpenGL, it always shows lags/jitters (lost of frames). But, running in
a fullscreen mode seems to solve the program in SDL 1.2

My question is how would we solve the jitters/lags problem in SDL2.0. Do we
use a fullscreen mode?

Thanks in advance