[SDL] Re: X11 again

Pierre Phaneuf pphaneuf at sx.nec.com
Wed Apr 5 08:59:00 PDT 2000


Benno Senoner wrote:

> - a set of drivers  which allows full direct access to 2D hardware,
> without any intervention of the X server (since the X server is run
> with SCHED_OTHER as a regular process, and performance will suck when
> you stress your system with other background load). Maybe the ideal
> situation would be a set functions to get access (mmap,DMA) to
> the gfx card's framebuffer mem, but not implemented as a
> client/server system but as a library, that means a SCHED_FIFO
> process (realtime-process) (assuming the low-latency extensions get
> into the official kernel) would receive full graphics performance ,
> no matter if you have heavy system load in the background or not.
> Of course these accelerations would be really nice in windowed-mode
> too, (with the method described above,manaul clipping), so that the
> user experiences full performance , independently from the fact
> whether he is working in fullscreen mode or not.

DGA will mmap the framebuffer, but everything else goes through the X
server. For things like an accelerator call for a large blit, I think
that it isn't that bad to have the X server do the call, but I think
this is because things currently sucks so much that I would be please
with little (like SOME acceleration).

I think that all the versions of DGA are restricted to full-screen.

What is *really* interesting is that new DRM module in the 2.3.x
kernel... Hmm... This is exactly how direct rendering works: the DRM
module allows the X client to do mmap/DMA to the video hardware (with
authorization from the X server), letting it do its own clipping for
windowed mode. This also means that a full duplicate of the video driver
has to be available to the X client, but this can be hidden in a library
(like libdri.so does).

-- 
Pierre Phaneuf
Systems Exorcist



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