Re: Vramfs: filesystem driver to utilize extra RAM on VGA devices

[Eric Anholt]

On Mon, 2009-01-26 at 18:59 -0800, Mark Knecht wrote:
> On Mon, Jan 26, 2009 at 3:20 PM, Jonathan Campbell <jon@xxxxxxxxxxxxxxx> wrote:
> > Hey guys.
> > About a month ago while covered in the Seattle snowstorm I hacked together
> > this pseudofilesystem that might be of interest.
> >
> > I thought that this driver could solve two issues that I have:
> >
> > one, that today's graphics cards have relatively obscene amounts of RAM on
> > them even if you're not using it. If you're running it as a server and not
> > using it for 3D graphics, why not mount the VRAM on the graphics card as a
> > filesystem and store things there to get some extra space?
> >
> > two, if 3D hardware acceleration and access to GPU or texture memory could
> > be provided to user-space, one way to do it would be to provide sections of
> > VRAM as a filesystem that most languages (yes---even Perl!) could use to
> > work with todays graphics cards. They could treat the texture memory the way
> > they treat files in /dev/shm: read/write it for general access or mmap it
> > for direct manipulation. At least, it makes far more sense to me from a
> > programming point of view than to abstract it using specialized ioctls
> > through the DRI. It might make writing an OpenGL driver for this kind of
> > arrangement cleaner, too.
> >
> > http://www.nerdgrounds.com/vramfs-20090126-1458.tar.gz
> >
> > So far I've tested it against 2.6.25.17 and 2.6.28 on both x86 and x86_64
> > with reads, writes, directory creation, symlink creation, and mmap() and it
> > seems to work fine.
> > Just give it a range of memory on the bus, or the domain:bus:device:function
> > numbers of a VGA PCI device, and it will mount the VGA video RAM and allow
> > files to exist there.
> > As a special hack: you can also specify the size of the active framebuffer
> > console so that fbcon doesn't collide with this driver (unless you want to
> > see what your files look like splattered across your screen, ha). The active
> > VRAM area becomes a "sentinel" file named "framebuffer".
> >
> > What do you guys think?
> >
> > Jonathan Campbell
> > Impact Studio Pro
> >
> 
> Can the GPU use the data placed in your file system? Do you have
> strong control as to exactly how the data is mapped into VRAM? I'm
> thinking about parallel processing  - Linux puts data there and then
> the GPU works on it to produce a result which Linux can eventually
> fetch.

For that you want something like GEM, which is aware of the graphics
pipeline and the cache management necessary.  Wrapping a filesystem
around it shouldn't be hard, and would be of some use for debugging.

-- 
Eric Anholt
eric@xxxxxxxxxx                         eric.anholt@xxxxxxxxx

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