very slow performance of glxgears (68 fps)

Jim Gettys jg at
Thu Feb 19 06:44:35 PST 2009

On Thu, 2009-02-19 at 13:03 +0100, Matthias Hopf wrote:
> On Feb 18, 09 12:58:49 -0500, Jim Gettys wrote:
> > On Wed, 2009-02-18 at 10:49 -0700, McDonald, Michael-p7438c wrote:
> > > Dumb question: Do LCD/Plasma/OLED/... Actually have vertical retrace?
> > > Does the vblank interval approach 0?
> > 
> > LCD: yes
> > Plasma: yes
> > OLED: ?		(still mostly vaporware, and I'm sure compatibility means it
> > would have this characteristic at the moment, even if the technology
> > doesn't).
> You will always have the vertical retrace of the signal lane (read:
> TMDS, LVDS, or VGA). Unless you have a massively parallel RAM readout
> and connection to the display ;-)

The reason I waffled is that there are good reasons to have the image
stored out in the display (power in particular; the fewer pixels that
change, the less you flap high capacitance lines. Driving those lines
right now has become a significant part of overall system power usage).
And future interfaces (DisplayPort, IIRC) to displays are capable of
updating pixels independently (usually a specified rectangle).    So if
memory is right by the pixels the concept of vertical retrace may become
moot, conceivably, someday.

I agree this hasn't happened (yet).
                         - Jim

Jim Gettys <jg at>

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