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

[Mark Knecht <markknecht@gmail.com>]

On Mon, Jan 26, 2009 at 9:07 PM, Jonathan Campbell <jon@nerdgrounds.com> wrote:
>
>> Can the GPU use the data placed in your file system?
>
> Assuming the GPU can access any part of VRAM, yes. Files created in vramfs
> will always have content that exists somewhere in video ram. A file you
> create never moves, and is always contiguous in memory. All your program
> needs to direct the GPU to it is the block offset from the start of VRAM,
> which can be obtained by an ioctl() or bmap().
>
> I thought the best possible design would be for any process to create a file
> in vramfs, and then direct the attention of whoever's managing the GPU to
> that file (perhaps a user-space daemon), who could open the file and use
> bmap or an ioctl to locate it and direct the GPU to operate on it.
>

Yep, as I said in the response to Eric a number of us had talked in
the past about using the GPU for some audio operations that are just
too CPU intensive - reverb, multi-band compressors, etc. See Jamin as
an example of a great app that brings most DAW type boxes to their
knees.

http://jamin.sourceforge.net/en/about.html

> I'd also like to point out the filesystem structures themselves are never
> placed in VRAM on purpose. I'd hate for files to suddenly disappear from the
> filesystem because of an errant GPU bug or pixel shader gone amok; the worst
> that can happen by doing it that way is that a bunch of files go blank or
> get filled with garbage and no harm done.
>>
>> Do you have strong control as to exactly how the data is mapped into VRAM?
>
> Not exactly. When you create a file you get whatever free space is
> available. However, vramfs does guarantee that your file is never
> fragmented, never sparse, and will always exist for the life of the file
> from it's offset in video ram to the offset plus the file size. I believe
> I've written the code to be flexible enough however to allow stronger
> control if needed.

So what happens to the file system if the user changes screen
resolution, color depth, etc.? There must be features to manage stuff
like that?

- Mark