- IRIX 5.0:  It was reported that perfly would cause an Onyx RE or
    VTX to hang.  This was fixed in 5.0.1.

  - IRIX 5.0.1:  perfly would generate floating point exceptions due
    to a bug in the font manager library (libfm).  This was fixed in
    5.1.

  - IRIX 5.2/5.3 Kernel Panic:  Certain IRIX patches were
    incompatible with Performer and would cause the Town or Village
    demos to panic the system if run as root.  The error message
    was:

        PANIC: CPU 3: Stack Extension Page is inconsistent
        Double PANIC: CPU 0: Stack Extension Page is inconsistent 111
        at block 0

    In IRIX 5.2, the crash occurs with patches 125 and 139.
    In IRIX 5.3, the crash occurs with patch 158.

  - Jerky forward motion.  This is caused by an uneven frame rate.
    The Performer town demo is fill limited and typically can not
    maintain a steady 30Hz.

    This can also occur if perfly is not being run as root.  When run
    by root, Performer applications will set nondegradable priorities
    for their processes to improve the consistency of the run-time
    behavior.

    This same problem is also caused by the user having another
    GL-based application (like gr_osview) running at the same time.

  - Ghosting.  A true FAQ is why multiple images of objects like
    trees, house edges, the horizon, etc. are seen as the viewer
    turns.  This is a form of "temporal aliasing" and is an attribute
    of having a frame rate which is less than the video refresh
    rate.

    The problem is that a single image is scanned out onto the
    monitor several times before being changed.  The repetition of a
    frame means that the image is temporally inaccurate for motion.
    Real moving objects do not stay in one place for a couple frame
    times and then move.

    What's actually happening is that your eye is following an
    object, moving with the same angular velocity, which keeps the
    image stationary on the retina.  Between two video refreshes of
    the same frame, your eye has moved, but the image on the screen
    has not.  Consequently the image of the second frame appears at a
    different location on the retina, and you see a "ghost" image.

    So a simulation running at 20Hz update on a display refreshing at
    60Hz, the object will appear tripled.  On large objects such as
    horizon silhouette, the effect manifests itself as multiple
    edges.