[Xcb] OpenGL applications spends 20% of CPU-cycles in discard_reply

[Clemens Eisserer]

Hi,

I am currently working on an OpenGL based application which streams
video content asynchronously to the GPU.
For simplicity I am using freeglut3 as "toolkit".

When running the application I get quite a strange profile, a serious
amount of time is spent in the function "discard_reply" contained in
libxcb:

samples  %        image name               app name                 symbol name
3665     17.5401  libxcb.so.1.1.0          streamapp
discard_reply

Unfourtunately even with callgraph profiling I don't get any helpful
information:

-------------------------------------------------------------------------------
  3670     100.000  libxcb.so.1.1.0          testprog
xcb_discard_reply
3665     17.5401  libxcb.so.1.1.0          testprog
discard_reply
  3665     99.8638  libxcb.so.1.1.0          testprog
discard_reply [self]

Ideas how to track this issue down, would be very welcome.

Thank you in advance, Clemens