NVIDIA binary driver with rt patch

NVIDIA binary driver with rt patch

[Tom Cook]

I'm quite new to linux-rt.  I'm trying to get a usable RT kernel on an
Ubuntu 11.10 system.  It has an nVidia Quadro NVS 285 video card and
I'm trying to get the binary drivers working, too.

I've built the 3.0.25 kernel with the rt44 patcheset applied.  I've
also modified it slightly so that migrate_enable, migrate_disable and
__init_rt_mutex are exported using EXPORT_SYMBOL rather than
EXPORT_SYMBOL_GPL (note I am aware of the legal issues surrounding
this and won't be distributing the resulting kernel or source).  I've
then patched the nVidia driver source, replacing atomic_spinlock with
raw_spinlock, down/up with mutex_lock/mutex_unlock and semaphores with
mutexes.

The resulting system runs and has quite good RT performance (max
latency <20us reported by cyclictest, at least on short tests with
full Ubuntu desktop running).  However, the performance of X is dire -
I get about two screen updates per second.  The mouse still moves
smoothly, but everything else only updates once or twice per second.
It seems to be something quite far down the graphics processing chain
that is slow, not individual operations - for instance, opening a page
in Firefox doesn't take much longer than usual, it's just that I get
no response at all for nearly a second and then the rendered page
appears.  It's like the screen is rendered into a buffer very fast but
then flipping that buffer to the display is very slow.

Does anyone have any suggestions for what might cause this or tools
for tracking down where the problem comes from?  I've spent a couple
of days googling now with no success.

Thanks for any help,
Tom

Re: NVIDIA binary driver with rt patch

[Thomas Schauss]

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On 04/04/2012 05:37 PM, Tom Cook wrote:
> I'm quite new to linux-rt.  I'm trying to get a usable RT kernel on an
> Ubuntu 11.10 system.  It has an nVidia Quadro NVS 285 video card and
> I'm trying to get the binary drivers working, too.
>
> I've built the 3.0.25 kernel with the rt44 patcheset applied.  I've
> also modified it slightly so that migrate_enable, migrate_disable and
> __init_rt_mutex are exported using EXPORT_SYMBOL rather than
> EXPORT_SYMBOL_GPL (note I am aware of the legal issues surrounding
> this and won't be distributing the resulting kernel or source).  I've
> then patched the nVidia driver source, replacing atomic_spinlock with
> raw_spinlock, down/up with mutex_lock/mutex_unlock and semaphores with
> mutexes.
>
> The resulting system runs and has quite good RT performance (max
> latency<20us reported by cyclictest, at least on short tests with
> full Ubuntu desktop running).  However, the performance of X is dire -
> I get about two screen updates per second.  The mouse still moves
> smoothly, but everything else only updates once or twice per second.
> It seems to be something quite far down the graphics processing chain
> that is slow, not individual operations - for instance, opening a page
> in Firefox doesn't take much longer than usual, it's just that I get
> no response at all for nearly a second and then the rendered page
> appears.  It's like the screen is rendered into a buffer very fast but
> then flipping that buffer to the display is very slow.
>
> Does anyone have any suggestions for what might cause this or tools
> for tracking down where the problem comes from?  I've spent a couple
> of days googling now with no success.
>
> Thanks for any help,
> Tom
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Hello Tom,

there was a thread about NVIDIA with linux-3.0-rt on this list some time 
back. The EXPORT_SYMBOL_GPL  hack is actually not necessary. If you make 
the appropriate changes to the nvidia-driver migrate enable/disable and 
other GPL-only exports are never called!

See this post for a patch that we use:
http://www.spinics.net/lists/linux-rt-users/msg07217.html

We have been using this on Ubuntu 11.10 for some time now. However, 
there are some compatibility issues with older NVIDIA-chips (computer 
freezes when starting X). I have not tries using this 
kernel/driver-combo for a Quatro-card yet so I am not sure if that works ok.

However, we never had the situation you are describing: either the 
computer froze when starting X or it worked fine, but we never 
experienced any (noticable) rendering delays.

Best regards,
Thomas

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