On Tue, 2006-09-19 at 12:49 +0200, Thomas Hellström wrote: > Benjamin Herrenschmidt wrote: > > 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. > > > > > Yes, I think that's what happens. I know some Athlon chips had a big > issue with this some time ago. > > I notice there are special functions in <agp.h> to alloc / free GATT > pages, so the general idea might be to have a pool of uncached pages > in the future for powerpc? Even better would perhaps be to have pages > that aren't mapped for the kernel. (like highmem pages on x86).
Yes, that's exactly what I'm thinking about doing. However, this is only a problem for AGP. For objects that are in video memory but can also be moved back to main memory (what I call "evicted") under pressure by the memory manager, one thing I was wondering is, do we have to bother about cache settings at all ? That is, have them mapped non-cacheable when in vram and cacheable when in main memory. Is there any reason why there would be a problem with userland having the same buffer being sometimes cacheable and non-cacheable ? I don't think so as long as userland isn't using cache tricks and whatever primitive is used to do the copy to/from vram properly accounts for it. 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
