From 14826673247eaf36b16fd821fac27efa663f3fa6 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Fri, 8 Sep 2017 19:16:22 +0100
Subject: [PATCH] drm/i915: Only initialize partially filled pagetables
Git-commit: 14826673247eaf36b16fd821fac27efa663f3fa6
Patch-mainline: v4.15-rc1
References: FATE#322643 bsc#1055900

If we know that we will completely fill a pagetable (i.e. we are
inserting a complete set of 512 pages), we can skip prefilling that PT
with scratch entries. If we have to abort the insertion prior to writing
the real entries, we will teardown the pagetable and remove it from the
page directory (so that we will restart the allocation next time).

We could do similar tricks for the PD and PDP, but the likelihood of a
single insertion covering the entire 512 entries diminishes, as do the
cycle savings. The saving are even greater (relatively) when we are
preallocating page tables for huge pages, as then we never need to fill
the page table.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170908181622.17791-1-chris@chris-wilson.co.uk
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/gpu/drm/i915/i915_gem_gtt.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -1164,19 +1164,22 @@ static int gen8_ppgtt_alloc_pd(struct i9
 	unsigned int pde;
 
 	gen8_for_each_pde(pt, pd, start, length, pde) {
+		int count = gen8_pte_count(start, length);
+
 		if (pt == vm->scratch_pt) {
 			pt = alloc_pt(vm);
 			if (IS_ERR(pt))
 				goto unwind;
 
-			gen8_initialize_pt(vm, pt);
+			if (count < GEN8_PTES)
+				gen8_initialize_pt(vm, pt);
 
 			gen8_ppgtt_set_pde(vm, pd, pt, pde);
 			pd->used_pdes++;
 			GEM_BUG_ON(pd->used_pdes > I915_PDES);
 		}
 
-		pt->used_ptes += gen8_pte_count(start, length);
+		pt->used_ptes += count;
 	}
 	return 0;