On Thu, Oct 20, 2016 at 3:11 AM, Michel Dänzer <michel at daenzer.net> wrote: > On 19/10/16 07:33 PM, Marek Olšák wrote: >> On Wed, Oct 19, 2016 at 8:42 AM, Dave Airlie <airlied at gmail.com> wrote: >>> On 18 October 2016 at 23:53, Dan Williams <dan.j.williams at intel.com> wrote: >>>> On Mon, Oct 17, 2016 at 8:48 PM, Dave Airlie <airlied at gmail.com> wrote: >>>> [..] >>>>>>> Aren't there only 2 possibilities for this regression? >>>>>>> >>>>>>> 1/ a memtype entry was never made so track_pfn_insert() returns an >>>>>>> uncached mapping >>>>>>> >>>>>>> 2/ a conflicting memtype entry exists and undefined behavior due to >>>>>>> mixed mapping types is avoided with the change. >>>>>> >>>>>> 3/ The CPU usage through this path goes up, and slows things down, >>>>>> though I suspect you it's more an uncached mapping showing up >>>>>> when we don't expect it. >>>>> >>>>> It's looking line number 1, there is no mapping, now we get uncached >>>>> where we used to get write through. >>>>> >>>>> difference in page prot 7f7bbc0e0000, pfn 20000000000e71e4, >>>>> 8000000000000037, 800000000000002f >>>>> >>>>> 0x2f is the vma pg prot which has PWT set in it, 0x37 is the returned >>>>> pgprot which lacks that bit. >>>>> >>>>> not sure where to go from here, suggestions? >>>> >>>> If the driver established an ioremap_wt() across the range, or just >>>> called reserve_memtype() directly that should restore WT mappings. >>>> >>>> Although Daniel's suggestion to use the i915 mapping helpers sounds >>>> like it avoids problem 3/ as well. >>> >>> Well we shouldn't be doing that many VRAM mappings on the CPU so >>> I doubt we'll hit the overheads here that often. >>> >>> Ideally we'd always use DMA to move stuff in/out of VRAM, but there >>> are some places where we still do WC VRAM writes for uploads. >> >> WC VRAM for uploads is better than WC GART IMO. > > It's not a simple choice I'm afraid. While writing directly to WC VRAM > can be faster than writing to WC GART and then DMA'ing to VRAM, doing so > increases pressure on the first 256MB of VRAM. That's why I disabled > direct VRAM writes for streaming uploads again in > https://cgit.freedesktop.org/mesa/mesa/commit/?id=7b4276d7acf2e0f77044cb50caa6ad936fa78786 > . It's possible that something has changed since then though, feel free > to play with enabling it again. amdgpu should handle any memory pressure gracefully. radeon is not so robust though. Marek
