From: Matthew Auld matthew.auld@intel.com
commit 0abb33bfca0fb74df76aac03e90ce685016ef7be upstream.
We skip filling out the pt with scratch entries if the va range covers the entire pt, since we later have to fill it with the PTEs for the object pages anyway. However this might leave open a small window where the PTEs don't point to anything valid for the HW to consume.
When for example using 2M GTT pages this fill_px() showed up as being quite significant in perf measurements, and ends up being completely wasted since we ignore the pt and just use the pde directly.
Anyway, currently we have our PTE construction split between alloc and insert, which is probably slightly iffy nowadays, since the alloc doesn't actually allocate anything anymore, instead it just sets up the page directories and points the PTEs at the scratch page. Later when we do the insert step we re-program the PTEs again. Better might be to squash the alloc and insert into a single step, then bringing back this optimisation(along with some others) should be possible.
Fixes: 14826673247e ("drm/i915: Only initialize partially filled pagetables") Signed-off-by: Matthew Auld matthew.auld@intel.com Cc: Jon Bloomfield jon.bloomfield@intel.com Cc: Chris Wilson chris.p.wilson@intel.com Cc: Daniel Vetter daniel@ffwll.ch Cc: stable@vger.kernel.org # v4.15+ Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Link: https://patchwork.freedesktop.org/patch/msgid/20210713130431.2392740-1-matth... (cherry picked from commit 8f88ca76b3942d82e2c1cea8735ec368d89ecc15) Signed-off-by: Rodrigo Vivi rodrigo.vivi@intel.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/gpu/drm/i915/gt/gen8_ppgtt.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-)
--- a/drivers/gpu/drm/i915/gt/gen8_ppgtt.c +++ b/drivers/gpu/drm/i915/gt/gen8_ppgtt.c @@ -298,10 +298,7 @@ static void __gen8_ppgtt_alloc(struct i9 __i915_gem_object_pin_pages(pt->base); i915_gem_object_make_unshrinkable(pt->base);
- if (lvl || - gen8_pt_count(*start, end) < I915_PDES || - intel_vgpu_active(vm->i915)) - fill_px(pt, vm->scratch[lvl]->encode); + fill_px(pt, vm->scratch[lvl]->encode);
spin_lock(&pd->lock); if (likely(!pd->entry[idx])) {