[OpenJDK 2D-Dev] Disabling offscreen pixmaps by default?

[Dmitri Trembovetski]

   Hi Clemens,

Clemens Eisserer wrote:
> Hi,
> 
> Would it be possible to disable offscreen pixmaps by default when
> running the X11 pipeline and when the xserver is running locally and
> does not support SHMPIxmaps?

   Yes, we may have to do that.

   It can be done under this bug id:
     6708580: Java applications slow when EXA enabled

   If you would like to contribute the fix, be my guest =)

   We have the code to detect local x server, and whether the
   shared memory pixmaps are available - so should be relatively
   easy to implement..

   Thanks,
     Dmitri

> EXA based drivers (radeon/intel/nouveau) in general place pixmaps in
> VRAM which kills performance and don't support SHMPixmaps.
> 
> Yes, pmoffscreen is sometimes slower, but it avoids really horrible
> worst-case scenarious which happen on EXA based drivers.
> And because even antialiased text causes fallbacks, worst case is quite common.
> I ran some swing benchmarks, and results are horrible when running on
> top of EXA based drivers, a 5x slowdown is not uncommon here.
> 
> All major distributions now enable EXA by default, at least when using
> the intel-driver.
> I am not sure about radeon, but their EXA implementation is quite
> solid too - so sooner or later they will also use Exa by default if
> they do not already default to it.
> Finally the latest NVidia-Beta driver disables SHMPixmaps by default -
> however it has smarter migration heuristics which keep the pixmap in
> sysmem - only causing a ~2x slowdown.
> 
> - Clemens