On Tue, 2006-09-19 at 11:27 +0200, Thomas Hellström wrote: > But this should be the same problem encountered by the agpgart driver? > x86 and x86-64 calls change_page_attr() to take care of this. > On powerpc it is simply a noop. (<asm/agp.h>)
Possibly. We sort-of ignore the issue for now on PowerPC and happen to be lucky most of the time because 32 bits PowerPC aren't that agressive at prefetching... I haven't looked at change_page_attr() implementation on x86 but I know they also map the linear mapping with large pages. I don't know what happens if you start trying to change a single page attribute. x86 can breakup that large page into 4k pages, so maybe that's what happens. > Currently we take the following approach when the GPU needs access to > a buffer: > > 0) Take the hardware lock. > 1) The buffer is validated, and if not present in the GATT, it's > flipped in. At this point, idle buffers may be flipped out. > 2) The app submits a batch buffer (or in the general case a command > sequence). All buffers that are referenced by this command sequence > needs to have been validated, and the command sequence should be > updated with their new GATT offset. > 3) A "fence" is emitted, and associated with all unfenced buffers. > 4) The hardware lock is released. > 5) When the fence has expired (The GPU is finished with the command > sequence), the buffers associated with it may optionally be thrown > out. > > One problem is that buffers that need to be pinned (_always_ available > to the GPU) cannot be thrown out and will thus fragment the aperture- > or VRAM space. > > Buffers also carry usage- and mapping refcounts. They are not allowed > to be validated when mapped, and (except under some circumstances) are > not allowed to be mapped while validated. Buffer destruction occurs > when the refcount goes to zero. Yup. My idea was to allow the locking from userspace to allow for chips that can allow userspace direct command submission. Basically, lock/pin the buffer if it's still in the card, and if that fails (because it's been evicted already), then fallback to a kernel call. Ben. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys -- and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel
