[PATCH 7/7] drm/i915/gem: Bind the fence async for execbuf

Chris Wilson chris at chris-wilson.co.uk
Tue Apr 7 07:59:52 UTC 2020


It is illegal to wait on an another vma while holding the vm->mutex, as
that easily leads to ABBA deadlocks (we wait on a second vma that waits
on us to release the vm->mutex). So while the vm->mutex exists, move the
waiting outside of the lock into the async binding pipeline.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 .../gpu/drm/i915/gem/i915_gem_execbuffer.c    |  21 ++-
 drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c  | 122 +++++++++++++++++-
 drivers/gpu/drm/i915/gt/intel_ggtt_fencing.h  |   5 +
 3 files changed, 138 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
index ea05646193fb..d3896e63c296 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
@@ -509,13 +509,19 @@ eb_pin_vma(struct i915_execbuffer *eb,
 	}
 
 	if (unlikely(ev->flags & EXEC_OBJECT_NEEDS_FENCE)) {
-		if (unlikely(i915_vma_pin_fence(vma))) {
-			i915_vma_unpin(vma);
-			return false;
-		}
+		struct i915_fence_reg *reg = vma->fence;
 
-		if (vma->fence)
+		/* Avoid waiting to change the fence; defer to async worker */
+		if (reg) {
+			if (READ_ONCE(reg->dirty))
+				return false;
+
+			atomic_inc(&reg->pin_count);
 			ev->flags |= __EXEC_OBJECT_HAS_FENCE;
+		} else {
+			if (i915_gem_object_is_tiled(vma->obj))
+				return false;
+		}
 	}
 
 	ev->flags |= __EXEC_OBJECT_HAS_PIN;
@@ -962,7 +968,7 @@ static int eb_reserve_vma(struct eb_vm_work *work, struct eb_vma *ev)
 
 pin:
 	if (unlikely(exec_flags & EXEC_OBJECT_NEEDS_FENCE)) {
-		err = __i915_vma_pin_fence(vma); /* XXX no waiting */
+		err = __i915_vma_pin_fence_async(vma, &work->base);
 		if (unlikely(err))
 			return err;
 
@@ -1038,6 +1044,9 @@ static int eb_bind_vma(struct dma_fence_work *base)
 
 		GEM_BUG_ON(vma->vm != vm);
 
+		if (ev->flags & __EXEC_OBJECT_HAS_FENCE)
+			__i915_vma_apply_fence_async(vma);
+
 		if (!ev->bind_flags)
 			goto put;
 
diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c b/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c
index 7fb36b12fe7a..473af638d432 100644
--- a/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c
+++ b/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c
@@ -21,10 +21,13 @@
  * IN THE SOFTWARE.
  */
 
+#include "i915_active.h"
 #include "i915_drv.h"
 #include "i915_scatterlist.h"
+#include "i915_sw_fence_work.h"
 #include "i915_pvinfo.h"
 #include "i915_vgpu.h"
+#include "i915_vma.h"
 
 /**
  * DOC: fence register handling
@@ -343,16 +346,14 @@ static struct i915_fence_reg *fence_find(struct i915_ggtt *ggtt)
 int __i915_vma_pin_fence(struct i915_vma *vma)
 {
 	struct i915_ggtt *ggtt = i915_vm_to_ggtt(vma->vm);
-	struct i915_fence_reg *fence;
+	struct i915_fence_reg *fence = vma->fence;
 	struct i915_vma *set = i915_gem_object_is_tiled(vma->obj) ? vma : NULL;
 	int err;
 
 	lockdep_assert_held(&vma->vm->mutex);
 
 	/* Just update our place in the LRU if our fence is getting reused. */
-	if (vma->fence) {
-		fence = vma->fence;
-		GEM_BUG_ON(fence->vma != vma);
+	if (fence && fence->vma == vma) {
 		atomic_inc(&fence->pin_count);
 		if (!fence->dirty) {
 			list_move_tail(&fence->link, &ggtt->fence_list);
@@ -384,6 +385,119 @@ int __i915_vma_pin_fence(struct i915_vma *vma)
 	return err;
 }
 
+static int set_bind_fence(struct i915_fence_reg *fence,
+			  struct dma_fence_work *work)
+{
+	struct dma_fence *prev;
+	int err;
+
+	if (rcu_access_pointer(fence->active.excl.fence) == &work->dma)
+		return 0;
+
+	if (i915_active_acquire(&fence->active))
+		return -ENOENT;
+
+	err = i915_sw_fence_await_active(&work->chain,
+					 &fence->active,
+					 I915_ACTIVE_AWAIT_ACTIVE);
+	if (err)
+		goto out;
+
+	prev = i915_active_set_exclusive(&fence->active, &work->dma);
+	if (unlikely(prev)) {
+		err = i915_sw_fence_await_dma_fence(&work->chain, prev, 0,
+						    GFP_NOWAIT | __GFP_NOWARN);
+		dma_fence_put(prev);
+	}
+
+out:
+	i915_active_release(&fence->active);
+	return err < 0 ? err : 0;
+}
+
+int __i915_vma_pin_fence_async(struct i915_vma *vma,
+			       struct dma_fence_work *work)
+{
+	struct i915_ggtt *ggtt = i915_vm_to_ggtt(vma->vm);
+	struct i915_vma *set = i915_gem_object_is_tiled(vma->obj) ? vma : NULL;
+	struct i915_fence_reg *fence = vma->fence;
+	int err;
+
+	lockdep_assert_held(&vma->vm->mutex);
+
+	/* Just update our place in the LRU if our fence is getting reused. */
+	if (fence && fence->vma == vma) {
+	} else if (set) {
+		fence = fence_find(ggtt);
+		if (IS_ERR(fence))
+			return PTR_ERR(fence);
+
+		GEM_BUG_ON(atomic_read(&fence->pin_count));
+		fence->dirty = true;
+	} else {
+		return 0;
+	}
+
+	atomic_inc(&fence->pin_count);
+	if (!fence->dirty) {
+		list_move_tail(&fence->link, &ggtt->fence_list);
+		return 0;
+	}
+
+	fence->tiling = 0;
+	if (set) {
+		if (!i915_vma_is_map_and_fenceable(vma)) {
+			err = -EINVAL;
+			goto err_unpin;
+		}
+
+		if (INTEL_GEN(fence_to_i915(fence)) < 4 &&
+		    rcu_access_pointer(vma->active.excl.fence) != &work->dma) {
+			/* implicit 'unfenced' GPU blits */
+			err = i915_sw_fence_await_active(&work->chain,
+							 &vma->active,
+							 I915_ACTIVE_AWAIT_ACTIVE);
+			if (err)
+				goto err_unpin;
+		}
+
+		fence->start = vma->node.start;
+		fence->size = vma->fence_size;
+		fence->stride = i915_gem_object_get_stride(vma->obj);
+		fence->tiling = i915_gem_object_get_tiling(vma->obj);
+	}
+
+	set = xchg(&fence->vma, vma);
+	if (set) {
+		err = set_bind_fence(fence, work);
+		if (err) {
+			fence->vma = set;
+			goto err_unpin;
+		}
+
+		if (set != vma) {
+			GEM_BUG_ON(set->fence != fence);
+			i915_vma_revoke_mmap(set);
+			set->fence = NULL;
+		}
+	}
+
+	vma->fence = fence;
+	return 0;
+
+err_unpin:
+	atomic_dec(&fence->pin_count);
+	return err;
+}
+
+void __i915_vma_apply_fence_async(struct i915_vma *vma)
+{
+	struct i915_fence_reg *fence = vma->fence;
+
+	if (fence->dirty)
+		fence_write(fence);
+}
+
 /**
  * i915_vma_pin_fence - set up fencing for a vma
  * @vma: vma to map through a fence reg
diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.h b/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.h
index 9eef679e1311..d306ac14d47e 100644
--- a/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.h
+++ b/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.h
@@ -30,6 +30,7 @@
 
 #include "i915_active.h"
 
+struct dma_fence_work;
 struct drm_i915_gem_object;
 struct i915_ggtt;
 struct i915_vma;
@@ -70,6 +71,10 @@ void i915_gem_object_do_bit_17_swizzle(struct drm_i915_gem_object *obj,
 void i915_gem_object_save_bit_17_swizzle(struct drm_i915_gem_object *obj,
 					 struct sg_table *pages);
 
+int __i915_vma_pin_fence_async(struct i915_vma *vma,
+			       struct dma_fence_work *work);
+void __i915_vma_apply_fence_async(struct i915_vma *vma);
+
 void intel_ggtt_init_fences(struct i915_ggtt *ggtt);
 void intel_ggtt_fini_fences(struct i915_ggtt *ggtt);
 
-- 
2.20.1



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