[PATCH 6/9] drm/amdgpu: Set/clear CPU_ACCESS_REQUIRED flag on page fault and CS

[John Brooks]

When the AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED flag is given by userspace,
it should only be treated as a hint to initially place a BO somewhere CPU
accessible, rather than having a permanent effect on BO placement.

Instead of the flag being set in stone at BO creation, set the flag when a
page fault occurs so that it goes somewhere CPU-visible, and clear it when
the BO is requested by the GPU.

However, clearing the CPU_ACCESS_REQUIRED flag may move a BO to invisible
VRAM, which is likely to cause a page fault that moves it right back to
GTT. When this happens too much, it is highly detrimental to performance.
Only clear the flag on CS if:

- The BO wasn't page faulted for a certain amount of time (currently 10
  seconds, measured with jiffies), and
- its last page fault didn't occur too soon (currently 500ms) after its
  last CS request, or vice versa.

Setting the flag in amdgpu_fault_reserve_notify() also means that we can
remove the loop to restrict lpfn to the end of visible VRAM, because
amdgpu_ttm_placement_init() will do it for us.

Signed-off-by: John Brooks <john at fastquake.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c     |  1 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_object.c | 46 ++++++++++++++++++++++--------
 drivers/gpu/drm/amd/amdgpu/amdgpu_object.h |  1 +
 3 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
index 2fad8bd..73d6882 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
@@ -320,6 +320,7 @@ static int amdgpu_cs_bo_validate(struct amdgpu_cs_parser *p,
 	else
 		domain = bo->allowed_domains;
 
+	amdgpu_bo_clear_cpu_access_required(bo);
 retry:
 	amdgpu_ttm_placement_from_domain(bo, domain);
 	initial_bytes_moved = atomic64_read(&adev->num_bytes_moved);
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
index 31d1f21..a7d48a7 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.c
@@ -967,8 +967,8 @@ int amdgpu_bo_fault_reserve_notify(struct ttm_buffer_object *bo)
 {
 	struct amdgpu_device *adev = amdgpu_ttm_adev(bo->bdev);
 	struct amdgpu_bo *abo;
-	unsigned long offset, size, lpfn;
-	int i, r;
+	unsigned long offset, size;
+	int r;
 
 	if (!amdgpu_ttm_bo_is_amdgpu_bo(bo))
 		return 0;
@@ -991,18 +991,9 @@ int amdgpu_bo_fault_reserve_notify(struct ttm_buffer_object *bo)
 
 	/* hurrah the memory is not visible ! */
 	atomic64_inc(&adev->num_vram_cpu_page_faults);
+	abo->flags |= AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
 	amdgpu_ttm_placement_from_domain(abo, AMDGPU_GEM_DOMAIN_VRAM |
 					 AMDGPU_GEM_DOMAIN_GTT);
-	lpfn =	adev->mc.visible_vram_size >> PAGE_SHIFT;
-	for (i = 0; i < abo->placement.num_placement; i++) {
-		/* Try to move the BO into visible VRAM */
-		if ((abo->placements[i].flags & TTM_PL_FLAG_VRAM) &&
-		    (!abo->placements[i].lpfn ||
-		     abo->placements[i].lpfn > lpfn))
-			abo->placements[i].lpfn = lpfn;
-	}
-	abo->placement.busy_placement = abo->placement.placement;
-	abo->placement.num_busy_placement = abo->placement.num_placement;
 	r = ttm_bo_validate(bo, &abo->placement, false, false);
 	if (unlikely(r != 0))
 		return r;
@@ -1057,3 +1048,34 @@ u64 amdgpu_bo_gpu_offset(struct amdgpu_bo *bo)
 
 	return bo->tbo.offset;
 }
+
+/**
+ * amdgpu_bo_clear_cpu_access_required
+ * @bo: BO to update
+ *
+ * Clears CPU_ACCESS_REQUIRED flag if the BO hasn't had a page fault in a while
+ * and it didn't have a page fault too soon after the last time it was moved to
+ * VRAM.
+ *
+ * Caller should have bo reserved.
+ *
+ */
+void amdgpu_bo_clear_cpu_access_required(struct amdgpu_bo *bo)
+{
+	const unsigned int page_fault_timeout_ms = 10000;
+	const unsigned int min_period_ms = 500;
+	unsigned int ms_since_pf, period_ms;
+
+	ms_since_pf = jiffies_to_msecs(jiffies - bo->last_page_fault_jiffies);
+	period_ms = jiffies_to_msecs(abs(bo->last_page_fault_jiffies -
+					 bo->last_cs_move_jiffies));
+
+	/*
+	 * Try to avoid a revolving door between GTT and VRAM. Clearing the
+	 * flag may move this BO back to VRAM, so don't clear it if it's likely
+	 * to page fault and go right back to GTT.
+	 */
+	if ((!bo->last_page_fault_jiffies || !bo->last_cs_move_jiffies) ||
+	    (ms_since_pf > page_fault_timeout_ms && period_ms > min_period_ms))
+		bo->flags &= ~AMDGPU_GEM_CREATE_CPU_ACCESS_REQUIRED;
+}
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
index 3824851..b0cb137 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_object.h
@@ -182,6 +182,7 @@ int amdgpu_bo_restore_from_shadow(struct amdgpu_device *adev,
 				  struct reservation_object *resv,
 				  struct dma_fence **fence,
 				  bool direct);
+void amdgpu_bo_clear_cpu_access_required(struct amdgpu_bo *bo);
 
 
 /*
-- 
2.7.4