Comment 3 for bug 1053141

from the radeon man page:

Option "SwapbuffersWait" "boolean"
              This option controls the behavior of glXSwapBuffers and glXCopy‐
              SubBufferMESA calls by GL applications. If enabled, the calls
              will avoid tearing by making sure the display scanline is out‐
              side of the area to be copied before the copy occurs. If dis‐
              abled, no scanline synchronization is performed, meaning tearing
              will likely occur. Note that when enabled, this option can
              adversely affect the framerate of applications that render
              frames at less than refresh rate.

              The default value is on.

Conclusion:
It is required that we sync the waveform frames somehow to the vertical blank
to a void an unpredictable delay of up to 16,6 ms @ 60 Hz Displays