[RFC 2/5] drm/amdgpu: Actually respect buffer migration budget

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>

Current code appears to live in a misconception that playing with buffer
allowed and preferred placements can control the decision on whether
backing store migration will be attempted or not.

Both from code inspection and from empirical experiments I see that not
being true, and that both allowed and preferred placement are typically
set to the same bitmask.

As such, when the code decides to throttle the migration for a client, it
is in fact not achieving anything. Buffers can still be either migrated or
not migrated based on the external (to this function and facility) logic.

Fix it by not changing the buffer object placements if the migration
budget has been spent.

FIXME:
Is it still required to call validate is the question..

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
Cc: Christian König <christian.koenig at amd.com>
Cc: Friedrich Vock <friedrich.vock at gmx.de>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
index 22708954ae68..d07a1dd7c880 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
@@ -784,6 +784,7 @@ static int amdgpu_cs_bo_validate(void *param, struct amdgpu_bo *bo)
 		.no_wait_gpu = false,
 		.resv = bo->tbo.base.resv
 	};
+	bool migration_allowed = true;
 	struct ttm_resource *old_res;
 	uint32_t domain;
 	int r;
@@ -805,19 +806,24 @@ static int amdgpu_cs_bo_validate(void *param, struct amdgpu_bo *bo)
 			 * visible VRAM if we've depleted our allowance to do
 			 * that.
 			 */
-			if (p->bytes_moved_vis < p->bytes_moved_vis_threshold)
+			if (p->bytes_moved_vis < p->bytes_moved_vis_threshold) {
 				domain = bo->preferred_domains;
-			else
+			} else {
 				domain = bo->allowed_domains;
+				migration_allowed = false;
+			}
 		} else {
 			domain = bo->preferred_domains;
 		}
 	} else {
 		domain = bo->allowed_domains;
+		migration_allowed = false;
 	}
 
 retry:
-	amdgpu_bo_placement_from_domain(bo, domain);
+	if (migration_allowed)
+		amdgpu_bo_placement_from_domain(bo, domain);
+
 	r = ttm_bo_validate(&bo->tbo, &bo->placement, &ctx);
 
 	if (unlikely(r == -ENOMEM) && domain != bo->allowed_domains) {
-- 
2.44.0