[vtk-developers] X11 and libGL always linked

[burlen]

Thanks Guys! I appreciate your eyes on it.

As you point out clearing OPENGL_gl_LIBRARY should prevent libGL 
dependency and link order issues. In my builds I have got into the habit 
of setting it to libOSMesa which does the same. In any case this doesn't 
prevent the X11 libs from being linked. in FindOpenGL.cmake that ships 
with cmake, X11 libs are always tacked onto OPENGL_LIBRARIES, which is 
used in Rendering/OpenGL/CMakeLists.

my main motivation in digging into these issues is to address a PV 
performance issue on NERSC's Crays. Users found that PV start-ups were 
sometimes taking a very long time (eg 30 min for 48 way parallel run). 
We tracked the issue to the file system and PV's use of shared 
libraries. With PV there are many shared library dependencies (~200), 
and when parallel pvserver's startup they all hit the file system at the 
same time all opening these shared library files. When I make static 
executables startup time is reduced reliably to a few seconds. I admit 
static executables are an extreme measure, and I hit a handful of 
cmake/pv specific cmake related issues doing it that won't be easy to 
address. However, it's probably OK performance wise to settle for "as 
static as possible", and getting the list of shared library dependencies 
from ~200 to ~10 should make for a big improvement. Removing those X11 
deps when using OSMesa gets us "as static as possible" and without too 
much effort.

Burlen

On 03/17/2014 08:03 AM, David E DeMarle wrote:
> I'll take a close look at this too.
>
> Like Andy said, we do get by for example in ParaView's cross compiling 
> super build, but I'm all in for making it easier in practice to get 
> VTK and ParaView up and running in HPC contexts.
>
> Thanks as always Burlen!
>
>
> David E DeMarle
> Kitware, Inc.
> R&D Engineer
> 21 Corporate Drive
> Clifton Park, NY 12065-8662
> Phone: 518-881-4909
>
>
> On Mon, Mar 17, 2014 at 10:06 AM, Marcus D. Hanwell 
> <marcus.hanwell at kitware.com <mailto:marcus.hanwell at kitware.com>> wrote:
>
>     On Fri, Mar 14, 2014 at 5:31 PM, Burlen Loring
>     <burlen.loring at gmail.com <mailto:burlen.loring at gmail.com>> wrote:
>     > Hi All,
>     >
>     > While installing the past two PV releases I've noticed that VTK
>     is linking
>     > in X11 and libGL when using OSMesa, which is acheived by
>     VTK_USE_X=OFF and
>     > VTK_OPENGL_HAS_OSMESA=ON. This is one a of a number of issues
>     that is making
>     > statically linked PV executables on the Cray painful. I think
>     that the
>     > history of this is that this was useful in the past when mangled
>     Mesa was
>     > used but currently this is the wrong thing to do because the
>     extension
>     > manager can only use one or the other as GetProcAddress function
>     is selected
>     > at compile time, and at run time it's used indiscriminatly
>     regardless of
>     > actual context type(OSMesa context or other GL context) so
>     there's currently
>     > no chance that you could safely use both. Also, linking both
>     libraries can
>     > create a link time race condition between libGL and libOSMesa
>     that depends
>     > on link order(eg both are .so's or .a's). I think that in a
>     single build VTK
>     > needs to carefully use either libGL or OSMesa, but not both, and
>     that
>     > linking against X11 should be avoided when VTK_USE_X11=OFF.
>      I've tracked
>     > the X11 library inclusion down, it's coming from
>     FindOpenGL.cmake, which
>     > appends X11 libraries to OPENGL_LIBRARIES indiscriminately when
>     X11 is
>     > found. I've pushed a patch (which needs a careful review and
>     some more
>     > testing) onto gerrit that explicitly separates OpenGL and OSMesa
>     use in
>     > VTK(http://review.source.kitware.com/#/c/14730/). I'd like to
>     know if others
>     > agree that this is a reasonable change? Thoughts and/or comments?
>     >
>     I started looking at this briefly before I left, and hit the same
>     thing Andy mentioned (having to clear OPENGL_gl_LIBRARY to get a
>     working OSMesa). It would be great to improve this part of the build
>     system (I wasn't aware of all the history, but assumed it had
>     something to do with mangled mesa).
>
>     I will try to find some time to take a closer look at the proposed
>     patch in the next few days, and always wanted to loop back to this
>     logic since modularization as it appeared overly complex but we also
>     wanted to remain cautious to breaking OSMesa/other build
>     configurations and it was largely ported from previous logic.
>
>     Marcus
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