On 04.09.2014 10:55, Jerome Glisse wrote: > > While i agree about the issue of incoherent double map of same page, i > think we have more issue. For instance lattely AMD have been pushing a > lot of patches to move things to use uncached memory for radeon and as > usual thoses patches comes with no comment to the motivations of those > changes.
That would have been a fair review comment... > What i understand is that uncached mapping for some frequently use buffer > give a significant performance boost (i am assuming this has to do with > all the snoop pci transaction overhead). Exactly, although it's a win even if the data is written by the CPU only once and read by the GPU only once. > This also means that we need to fix ttm_tt_set_placement_caching so that > when it returns an error it switches to cached mapping. Which will always > work. GTT with AGP being one exception. -- Earthling Michel D?nzer | http://www.amd.com Libre software enthusiast | Mesa and X developer
