Re: [PATCH 06/20] drm/i915: add I915_BO_ALLOC_TOPDOWN

Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx> · Mon, 31 Jan 2022 16:28:16 +0100

On 1/26/22 16:21, Matthew Auld wrote:
If the user doesn't require CPU access for the buffer, then
ALLOC_TOPDOWN should be used, in order to prioritise allocating in the
non-mappable portion of LMEM.

Signed-off-by: Matthew Auld <matthew.auld@xxxxxxxxx>
Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>

I was wondering how this would work best with user-space not supplying 
any hints. Thinking that mappable LMEM buffers would be a minority, 
wouldn't it be better to have TOPDOWN behaviour set by default. It would 
then be migrated to mappable only if needed. And if the first usage is a 
cpu-map it would either be mapped in system or immediately migrated from 
pageless to mappable LMEM?


---
  drivers/gpu/drm/i915/gem/i915_gem_object_types.h | 15 +++++++++++----
  drivers/gpu/drm/i915/gem/i915_gem_pages.c        |  3 +++
  drivers/gpu/drm/i915/gem/i915_gem_region.c       |  5 +++++
  drivers/gpu/drm/i915/gem/i915_gem_ttm.c          | 13 ++++++++++---
  drivers/gpu/drm/i915/gt/intel_gt.c               |  4 +++-
  drivers/gpu/drm/i915/i915_vma.c                  |  3 +++
  drivers/gpu/drm/i915/intel_region_ttm.c          | 11 ++++++++---
  drivers/gpu/drm/i915/selftests/mock_region.c     |  7 +------
  8 files changed, 44 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
index 71e778ecaeb8..29285aaf0477 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
@@ -319,15 +319,22 @@ struct drm_i915_gem_object {
  #define I915_BO_ALLOC_PM_VOLATILE BIT(4)
  /* Object needs to be restored early using memcpy during resume */
  #define I915_BO_ALLOC_PM_EARLY    BIT(5)
+/*
+ * Object is likely never accessed by the CPU. This will prioritise the BO to be
+ * allocated in the non-mappable portion of lmem. This is merely a hint, and if
+ * dealing with userspace objects the CPU fault handler is free to ignore this.
+ */
+#define I915_BO_ALLOC_TOPDOWN	  BIT(6)
  #define I915_BO_ALLOC_FLAGS (I915_BO_ALLOC_CONTIGUOUS | \
  			     I915_BO_ALLOC_VOLATILE | \
  			     I915_BO_ALLOC_CPU_CLEAR | \
  			     I915_BO_ALLOC_USER | \
  			     I915_BO_ALLOC_PM_VOLATILE | \
-			     I915_BO_ALLOC_PM_EARLY)
-#define I915_BO_READONLY          BIT(6)
-#define I915_TILING_QUIRK_BIT     7 /* unknown swizzling; do not release! */
-#define I915_BO_PROTECTED         BIT(8)
+			     I915_BO_ALLOC_PM_EARLY | \
+			     I915_BO_ALLOC_TOPDOWN)
+#define I915_BO_READONLY          BIT(7)
+#define I915_TILING_QUIRK_BIT     8 /* unknown swizzling; do not release! */
+#define I915_BO_PROTECTED         BIT(9)
  	/**
  	 * @mem_flags - Mutable placement-related flags
  	 *
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
index 7d2211fbe548..a95b4d72619f 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
@@ -346,6 +346,9 @@ void *i915_gem_object_pin_map(struct drm_i915_gem_object *obj,
  	    !i915_gem_object_has_iomem(obj))
  		return ERR_PTR(-ENXIO);
  
+	if (WARN_ON_ONCE(obj->flags & I915_BO_ALLOC_TOPDOWN))
+		return ERR_PTR(-EINVAL);
+
  	assert_object_held(obj);
  
  	pinned = !(type & I915_MAP_OVERRIDE);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_region.c b/drivers/gpu/drm/i915/gem/i915_gem_region.c
index a4350227e9ae..f91e5a9c759d 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_region.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_region.c
@@ -45,6 +45,11 @@ i915_gem_object_create_region(struct intel_memory_region *mem,
  
  	GEM_BUG_ON(flags & ~I915_BO_ALLOC_FLAGS);
  
+	if (WARN_ON_ONCE(flags & I915_BO_ALLOC_TOPDOWN &&
+			 (flags & I915_BO_ALLOC_CPU_CLEAR ||
+			  flags & I915_BO_ALLOC_PM_EARLY)))
+		return ERR_PTR(-EINVAL);
+
  	if (!mem)
  		return ERR_PTR(-ENODEV);
  
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
index d9a04c7d41b1..e60b677ecd54 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
@@ -127,10 +127,14 @@ i915_ttm_place_from_region(const struct intel_memory_region *mr,
  	place->mem_type = intel_region_to_ttm_type(mr);
  
  	if (flags & I915_BO_ALLOC_CONTIGUOUS)
-		place->flags = TTM_PL_FLAG_CONTIGUOUS;
+		place->flags |= TTM_PL_FLAG_CONTIGUOUS;
  	if (mr->io_size && mr->io_size < mr->total) {
-		place->fpfn = 0;
-		place->lpfn = mr->io_size >> PAGE_SHIFT;
+		if (flags & I915_BO_ALLOC_TOPDOWN) {
+			place->flags |= TTM_PL_FLAG_TOPDOWN;
+		} else {
+			place->fpfn = 0;
+			place->lpfn = mr->io_size >> PAGE_SHIFT;
+		}
  	}
  }
  
@@ -890,6 +894,9 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf)
  	if (!obj)
  		return VM_FAULT_SIGBUS;
  
+	if (obj->flags & I915_BO_ALLOC_TOPDOWN)
+		return -EINVAL;
+
  	/* Sanity check that we allow writing into this object */
  	if (unlikely(i915_gem_object_is_readonly(obj) &&
  		     area->vm_flags & VM_WRITE))
diff --git a/drivers/gpu/drm/i915/gt/intel_gt.c b/drivers/gpu/drm/i915/gt/intel_gt.c
index 622cdfed8a8b..8b83a771a2f7 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt.c
@@ -454,7 +454,9 @@ static int intel_gt_init_scratch(struct intel_gt *gt, unsigned int size)
  	struct i915_vma *vma;
  	int ret;
  
-	obj = i915_gem_object_create_lmem(i915, size, I915_BO_ALLOC_VOLATILE);
+	obj = i915_gem_object_create_lmem(i915, size,
+					  I915_BO_ALLOC_VOLATILE |
+					  I915_BO_ALLOC_TOPDOWN);
  	if (IS_ERR(obj))
  		obj = i915_gem_object_create_stolen(i915, size);
  	if (IS_ERR(obj))
diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index b1816a835abf..b2fdaa74e4b6 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -528,6 +528,9 @@ void __iomem *i915_vma_pin_iomap(struct i915_vma *vma)
  	void __iomem *ptr;
  	int err;
  
+	if (WARN_ON_ONCE(vma->obj->flags & I915_BO_ALLOC_TOPDOWN))
+		return IO_ERR_PTR(-EINVAL);
+
  	if (!i915_gem_object_is_lmem(vma->obj)) {
  		if (GEM_WARN_ON(!i915_vma_is_map_and_fenceable(vma))) {
  			err = -ENODEV;
diff --git a/drivers/gpu/drm/i915/intel_region_ttm.c b/drivers/gpu/drm/i915/intel_region_ttm.c
index 4689192d5e8d..282802aed174 100644
--- a/drivers/gpu/drm/i915/intel_region_ttm.c
+++ b/drivers/gpu/drm/i915/intel_region_ttm.c
@@ -199,13 +199,18 @@ intel_region_ttm_resource_alloc(struct intel_memory_region *mem,
  	struct ttm_resource *res;
  	int ret;
  
+	if (flags & I915_BO_ALLOC_CONTIGUOUS)
+		place.flags |= TTM_PL_FLAG_CONTIGUOUS;
  	if (mem->io_size && mem->io_size < mem->total) {
-		place.fpfn = 0;
-		place.lpfn = mem->io_size >> PAGE_SHIFT;
+		if (flags & I915_BO_ALLOC_TOPDOWN) {
+			place.flags |= TTM_PL_FLAG_TOPDOWN;
+		} else {
+			place.fpfn = 0;
+			place.lpfn = mem->io_size >> PAGE_SHIFT;
+		}
  	}
  
  	mock_bo.base.size = size;
-	place.flags = flags;
  
  	ret = man->func->alloc(man, &mock_bo, &place, &res);
  	if (ret == -ENOSPC)
diff --git a/drivers/gpu/drm/i915/selftests/mock_region.c b/drivers/gpu/drm/i915/selftests/mock_region.c
index 467eeae6d5f0..f64325491f35 100644
--- a/drivers/gpu/drm/i915/selftests/mock_region.c
+++ b/drivers/gpu/drm/i915/selftests/mock_region.c
@@ -22,17 +22,12 @@ static void mock_region_put_pages(struct drm_i915_gem_object *obj,
  
  static int mock_region_get_pages(struct drm_i915_gem_object *obj)
  {
-	unsigned int flags;
  	struct sg_table *pages;
  	int err;
  
-	flags = 0;
-	if (obj->flags & I915_BO_ALLOC_CONTIGUOUS)
-		flags |= TTM_PL_FLAG_CONTIGUOUS;
-
  	obj->mm.res = intel_region_ttm_resource_alloc(obj->mm.region,
  						      obj->base.size,
-						      flags);
+						      obj->flags);
  	if (IS_ERR(obj->mm.res))
  		return PTR_ERR(obj->mm.res);
  






