Re: Cygwin/X causes NVIDIA GPU to turn on in Optimus systems

[Jon TURNEY <jon.turney@dronecode.org.uk>]

On 26/03/2013 15:58, Aaron A. Kelley wrote:
> I usually leave Cygwin/X open on my machine because I use it to access GUI
> apps running in SSH terminals from time to time.  Today I noticed that in an
> Optimus environment, it is causing the NVIDIA GPU to kick in, which causes
> the NVIDIA GPU to stay powered on when maybe it doesnÂ’t need to.
> 
> http://stuff.aaron-kelley.net/2013/03/cygxoptimus.png
> 
> I went to the NVIDIA control panel and set xwin.exe specifically to use the
> integrated GPU but it still says that xwin.exe is running on the NVIDIA GPU
> when I run it.  Cygwin/X must be doing something unusual at initialization
> that makes the NVIDIA card feel like it has to kick on.  I donÂ’t have to
> actually launch any X windows to see this occur, it happens moments after I
> launch the Cygwin/X server.

The Cygwin X server doesn't do anything special (and specifically, doesn't do
any of the things listed in [1] to explicitly use the high-performance GPU),
so if it's being allowed to use OpenGL on the high-performance GPU despite the
application profile you have created, I would say that might be a bug in the
optimus driver.

Note that this policy does belong in your hands, not in XWin, as it cannot
know if you are going to be running any X programs using OpenGL, and if you
are, if you want high-performance rendering in them at the cost of additional
power usage.

As a workaround, you could start the X server with the -nowgl option added,
which should prevent any use of native OpenGL, forcing the use of software
rendering using mesa and see if that helps.

> I havenÂ’t been able to find anyone else mentioning this.  It may be because
> Optimus configurations arenÂ’t very common.  This also means that this issue
> may be tricky to track down.  IÂ’m not sure if it will be easy to find
> someone who knows about Cygwin/X development who also has access to an
> Optimus environment.  This might be something that has to go for NVIDIA for
> them to fix in their drivers, but itÂ’d be nice to know a little more about
> the issue before trying to get in touch with them.
> 
> IÂ’m interested in doing anything I can do help address this but I donÂ’t know
> where to begin, so IÂ’m welcoming your feedback.

For a start, you could look for the GL_VENDOR and GL_RENDERER lines in
/var/log/xwin/XWin.0.log to confirm that XWin also thinks it is using the
high-performance GPU.

[1]
http://developer.download.nvidia.com/devzone/devcenter/gamegraphics/files/OptimusRenderingPolicies.pdf

-- 
Jon TURNEY
Volunteer Cygwin/X X Server maintainer

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