Overhead of X?

Egbert Eich eich at suse.de
Wed Apr 19 04:16:15 PDT 2006

Bilderbeek, Manuel writes:
 > Hello all,
 > I have a simple general question about X.
 > I've been trying this on an 800x600x16bpp configured framebuffer: change
 > the screencolour with a memset. I can do this with about 90 fps. But
 > when I try this with a window in X, with the fbdev driver, I can get
 > only about 30fps. Is there so much overhead from X? 

X does a little more than just a memset() of the enitre framebuffer.
Filling the entire framebuffer with just one solid color is nothing that
the solid fill code in fb (that's what you are using unaccelerated) is
really optimized for. Therefore it will perform some tests and operations
that are not required for this particular operation.
This doesn't seem to be a very common use either.

Furthermore memset() is ususally higly optimized for your architecture.

This seems to be a poor comparison.


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