Bug#583653: xserver-xorg-video-radeon: 15x-slower performance regression in KMS mode for 2D operations

[Michel Dänzer]

On Mon, 2010-05-31 at 09:43 +0200, Michel Dänzer wrote: 
> reassign 583653 linux-2.6 2.6.32-13
> kthxbye
> 
> On Sam, 2010-05-29 at 17:33 +0200, Sylvain Beucler wrote: 
> > On Sat, May 29, 2010 at 04:21:46PM +0200, Michel Dänzer wrote:
> > > On Sam, 2010-05-29 at 15:02 +0200, Sylvain Beucler wrote: 
> > > > On Sat, May 29, 2010 at 01:05:36PM +0200, Michel Dänzer wrote:
> > > > > On Sam, 2010-05-29 at 10:21 +0200, Sylvain Beucler wrote: 
> > > > > > 
> > > > > > The attached simple test runs at 17FPS in KMS mode on my computer,
> > > > > > against 300FPS in non-KMS mode.
> > > > > 
> > > > > Forgot to mention: sysprof or oprofile profiles of slow and fast runs
> > > > > might be interesting, at least if the CPU is pegged during the runs.
> > > > 
> > > > Here are 2 sysprof runs:
> > > > - UMS / fast:
> > > >   - kernel 11.25%
> > > >   - X 77.20%
> > > > - KMS / slow:
> > > >   - kernel 90.28%
> > > >   - X 5.79%
> > > 
> > > Unfortunately, there's no information about where in the kernel the
> > > cycles are burnt. This information should be available with sysprof
> > > 1.1.x and a kernel with the performance counter/event framework.
> > 
> > Quite a nice tool:
> > 
> > __libc_start_main                                              0,00%  93,67%
> >   _start                                                       0,02%  87,66%
> >     In file /usr/bin/Xorg                                      0,13%  87,64%
> >       In file /usr/lib/xorg/modules/libexa.so                  0,04%  86,60%
> >         In file /usr/lib/xorg/modules/drivers/radeon_drv.so    0,08%  86,48%
> >           radeon_bo_open                                       0,00%  79,87%
> >             In file /usr/lib/libdrm_radeon.so.1.0.0            0,00%  79,87%
> >               drmCommandWriteRead                              0,00%  79,86%
> >                 __kernel_vsyscall                              0,00%  79,86%
> >                   - - kernel - -                               0,00%  79,86%
> >                     on_each_cpu                               36,81%  36,81%
> >                     __purge_vmap_area_lazy                    20,31%  20,31%
> >                     flush_all_zero_pkmaps                      7,84%   7,84%
> >                     vm_unmap_aliases                           1,65%   1,65%
> > 
> > What do you think that means?
> 
> I think it could confirm my suspicion below, reassigning to the kernel.
> Would be great if you could try if it's better with a 2.6.33 or 2.6.34
> kernel.
> 
> 
> > > Anyway, this probably means it's an issue in the kernel, not the X
> > > driver. May be solved already in newer kernels, there have been some AGP
> > > performance improvements which I'm not sure have made it into Debian's
> > > 2.6.32 DRM backport.

BTW, does booting the kernel with radeon.agpmode=-1 work around the
problem? It'll make things slower in general but it looks like it should
help for this problem, which would further confirm the above.


-- 
Earthling Michel Dänzer           |                http://www.vmware.com
Libre software enthusiast         |          Debian, X and DRI developer