Graphics speed depends on user profile

[Glynn Clements]

Juan Pablo de la Cruz wrote:

> We have an library which directly uses the Xlib API to do graphics.
> 
> We are observing the following effect: when two different users log
> in the same machine, use the same window manager, and run the very same
> program, the graphics are slower (much) for one of the users.
> 
> Concretely, the user for which the drawing is slower, logs himself in,
> and the other user executes su $USER on the terminal.
> 
> Both use the exact same libraries (same PATH and LD_LIBRARY_PATH).
> Both use the same window manager.
> 
> What other settings/factors could explain this behaviour?

What are their $DISPLAY settings?

If $DISPLAY is ":0" then the client will connect to the X server via
the Unix-domain socket at /tmp/.X11-unix/X0. Whereas if $DISPLAY is
"localhost:0", it will connect to the X server via TCP port 6000.

The latter will result in the data stream being chopped up into
packets and passed through the kernel's TCP/IP stack: routing,
firewall rules, etc.

It may also prevent the use of features such as direct rendering, as
the client and server are likely to be deemed to reside on different
systems.

-- 
Glynn Clements <glynn at gclements.plus.com>