[PATCH 25/27] drm/i915: Emit pipelined fence changes

Chris Wilson chris at chris-wilson.co.uk
Wed Aug 30 11:14:36 UTC 2017


Many years ago, long before requests, we tried doing this. We never
quite got it right, but now with requests we have the tracking to do the
job properly!

One of the stall points for gen2/gen3 is the use of fence registers for
GPU operations. There are only a few available, and currently if we
exhaust the available fence register we must stall the GPU between
batches. By pipelining the fence register writes, we can avoid the stall
and continuously emit the batches. The challenge is remembering to wait
for those pipelined LRI before accessing the fence with the CPU, and
that is what our request tracking makes easy.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gvt/aperture_gm.c     |   2 +-
 drivers/gpu/drm/i915/i915_debugfs.c        |   2 +-
 drivers/gpu/drm/i915/i915_gem.c            |   1 +
 drivers/gpu/drm/i915/i915_gem_execbuffer.c |  15 ++-
 drivers/gpu/drm/i915/i915_gem_fence_reg.c  | 206 ++++++++++++++++++++++++-----
 drivers/gpu/drm/i915/i915_gem_fence_reg.h  |   3 +-
 drivers/gpu/drm/i915/i915_vma.c            |   1 +
 drivers/gpu/drm/i915/i915_vma.h            |  13 +-
 8 files changed, 202 insertions(+), 41 deletions(-)

diff --git a/drivers/gpu/drm/i915/gvt/aperture_gm.c b/drivers/gpu/drm/i915/gvt/aperture_gm.c
index ca3d1925beda..3c835cb59d95 100644
--- a/drivers/gpu/drm/i915/gvt/aperture_gm.c
+++ b/drivers/gpu/drm/i915/gvt/aperture_gm.c
@@ -196,7 +196,7 @@ static int alloc_vgpu_fence(struct intel_vgpu *vgpu)
 	i = 0;
 	list_for_each_safe(pos, q, &dev_priv->mm.fence_list) {
 		reg = list_entry(pos, struct drm_i915_fence_reg, link);
-		if (reg->pin_count || reg->vma)
+		if (atomic_read(&reg->pin_count) || reg->vma)
 			continue;
 		list_del(pos);
 		vgpu->fence.regs[i] = reg;
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 86c516e780a6..34bfa7054183 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -917,7 +917,7 @@ static int i915_gem_fence_regs_info(struct seq_file *m, void *data)
 		struct i915_vma *vma = dev_priv->fence_regs[i].vma;
 
 		seq_printf(m, "Fence %d, pin count = %d, object = ",
-			   i, dev_priv->fence_regs[i].pin_count);
+			   i, atomic_read(&dev_priv->fence_regs[i].pin_count));
 		if (!vma)
 			seq_puts(m, "unused");
 		else
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index fa8434d78ce7..4989d265a5f3 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4928,6 +4928,7 @@ i915_gem_load_init_fences(struct drm_i915_private *dev_priv)
 		fence->i915 = dev_priv;
 		fence->id = i;
 		list_add_tail(&fence->link, &dev_priv->mm.fence_list);
+		init_request_active(&fence->pipelined, NULL);
 	}
 	i915_gem_restore_fences(dev_priv);
 
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 0509e1f8db17..32cb5493facf 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -366,11 +366,12 @@ eb_pin_vma(struct i915_execbuffer *eb,
 		return false;
 
 	if (unlikely(exec_flags & EXEC_OBJECT_NEEDS_FENCE)) {
-		if (unlikely(i915_vma_pin_fence(vma))) {
+		if (unlikely(i915_vma_reserve_fence(vma))) {
 			i915_vma_unpin(vma);
 			return false;
 		}
 
+		exec_flags &= ~EXEC_OBJECT_ASYNC;
 		if (vma->fence)
 			exec_flags |= __EXEC_OBJECT_HAS_FENCE;
 	}
@@ -562,12 +563,13 @@ static int eb_reserve_vma(const struct i915_execbuffer *eb,
 	}
 
 	if (unlikely(exec_flags & EXEC_OBJECT_NEEDS_FENCE)) {
-		err = i915_vma_pin_fence(vma);
+		err = i915_vma_reserve_fence(vma);
 		if (unlikely(err)) {
 			i915_vma_unpin(vma);
 			return err;
 		}
 
+		exec_flags &= ~EXEC_OBJECT_ASYNC;
 		if (vma->fence)
 			exec_flags |= __EXEC_OBJECT_HAS_FENCE;
 	}
@@ -1789,6 +1791,12 @@ static int eb_move_to_gpu(struct i915_execbuffer *eb)
 		if (flags & EXEC_OBJECT_ASYNC)
 			continue;
 
+		if (unlikely(flags & EXEC_OBJECT_NEEDS_FENCE)) {
+			err = i915_vma_emit_pipelined_fence(vma, eb->request);
+			if (err)
+				return err;
+		}
+
 		err = i915_gem_request_await_object
 			(eb->request, obj, flags & EXEC_OBJECT_WRITE);
 		if (err)
@@ -1875,9 +1883,6 @@ void i915_vma_move_to_active(struct i915_vma *vma,
 		obj->base.read_domains = 0;
 	}
 	obj->base.read_domains |= I915_GEM_GPU_DOMAINS;
-
-	if (flags & EXEC_OBJECT_NEEDS_FENCE)
-		i915_gem_active_set(&vma->last_fence, req);
 }
 
 static int i915_reset_gen7_sol_offsets(struct drm_i915_gem_request *req)
diff --git a/drivers/gpu/drm/i915/i915_gem_fence_reg.c b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
index 38fd077941d3..c5a00ff44786 100644
--- a/drivers/gpu/drm/i915/i915_gem_fence_reg.c
+++ b/drivers/gpu/drm/i915/i915_gem_fence_reg.c
@@ -55,10 +55,9 @@
  * CPU ptes into GTT mmaps (not the GTT ptes themselves) as needed.
  */
 
-#define pipelined 0
-
-static void i965_write_fence_reg(struct drm_i915_fence_reg *fence,
-				 struct i915_vma *vma)
+static int i965_write_fence_reg(struct drm_i915_fence_reg *fence,
+				struct i915_vma *vma,
+				struct drm_i915_gem_request *pipelined)
 {
 	i915_reg_t fence_reg_lo, fence_reg_hi;
 	int fence_pitch_shift;
@@ -110,11 +109,30 @@ static void i965_write_fence_reg(struct drm_i915_fence_reg *fence,
 		I915_WRITE(fence_reg_hi, upper_32_bits(val));
 		I915_WRITE(fence_reg_lo, lower_32_bits(val));
 		POSTING_READ(fence_reg_lo);
+	} else {
+		u32 *cs;
+
+		cs = intel_ring_begin(pipelined, 8);
+		if (IS_ERR(cs))
+			return PTR_ERR(cs);
+
+		*cs++ = MI_LOAD_REGISTER_IMM(3);
+		*cs++ = i915_mmio_reg_offset(fence_reg_lo);
+		*cs++ = 0;
+		*cs++ = i915_mmio_reg_offset(fence_reg_hi);
+		*cs++ = upper_32_bits(val);
+		*cs++ = i915_mmio_reg_offset(fence_reg_lo);
+		*cs++ = lower_32_bits(val);
+		*cs++ = MI_NOOP;
+		intel_ring_advance(pipelined, cs);
 	}
+
+	return 0;
 }
 
-static void i915_write_fence_reg(struct drm_i915_fence_reg *fence,
-				 struct i915_vma *vma)
+static int i915_write_fence_reg(struct drm_i915_fence_reg *fence,
+				struct i915_vma *vma,
+				struct drm_i915_gem_request *pipelined)
 {
 	u32 val;
 
@@ -150,11 +168,26 @@ static void i915_write_fence_reg(struct drm_i915_fence_reg *fence,
 
 		I915_WRITE(reg, val);
 		POSTING_READ(reg);
+	} else {
+		u32 *cs;
+
+		cs = intel_ring_begin(pipelined, 4);
+		if (IS_ERR(cs))
+			return PTR_ERR(cs);
+
+		*cs++ = MI_LOAD_REGISTER_IMM(1);
+		*cs++ = i915_mmio_reg_offset(FENCE_REG(fence->id));
+		*cs++ = val;
+		*cs++ = MI_NOOP;
+		intel_ring_advance(pipelined, cs);
 	}
+
+	return 0;
 }
 
-static void i830_write_fence_reg(struct drm_i915_fence_reg *fence,
-				 struct i915_vma *vma)
+static int i830_write_fence_reg(struct drm_i915_fence_reg *fence,
+				struct i915_vma *vma,
+				struct drm_i915_gem_request *pipelined)
 {
 	u32 val;
 
@@ -182,29 +215,49 @@ static void i830_write_fence_reg(struct drm_i915_fence_reg *fence,
 
 		I915_WRITE(reg, val);
 		POSTING_READ(reg);
+	} else {
+		u32 *cs;
+
+		cs = intel_ring_begin(pipelined, 4);
+		if (IS_ERR(cs))
+			return PTR_ERR(cs);
+
+		*cs++ = MI_LOAD_REGISTER_IMM(1);
+		*cs++ = i915_mmio_reg_offset(FENCE_REG(fence->id));
+		*cs++ = val;
+		*cs++ = MI_NOOP;
+		intel_ring_advance(pipelined, cs);
 	}
+
+	return 0;
 }
 
-static void fence_write(struct drm_i915_fence_reg *fence,
-			struct i915_vma *vma)
+static int fence_write(struct drm_i915_fence_reg *fence,
+		       struct i915_vma *vma,
+		       struct drm_i915_gem_request *rq)
 {
+	int err;
+
 	/* Previous access through the fence register is marshalled by
 	 * the mb() inside the fault handlers (i915_gem_release_mmaps)
 	 * and explicitly managed for internal users.
 	 */
 
 	if (IS_GEN2(fence->i915))
-		i830_write_fence_reg(fence, vma);
+		err = i830_write_fence_reg(fence, vma, rq);
 	else if (IS_GEN3(fence->i915))
-		i915_write_fence_reg(fence, vma);
+		err = i915_write_fence_reg(fence, vma, rq);
 	else
-		i965_write_fence_reg(fence, vma);
+		err = i965_write_fence_reg(fence, vma, rq);
+	if (err)
+		return err;
 
 	/* Access through the fenced region afterwards is
 	 * ordered by the posting reads whilst writing the registers.
 	 */
 
 	fence->dirty = false;
+	return 0;
 }
 
 static int fence_update(struct drm_i915_fence_reg *fence,
@@ -212,17 +265,15 @@ static int fence_update(struct drm_i915_fence_reg *fence,
 {
 	int ret;
 
+	ret = i915_gem_active_retire(&fence->pipelined,
+				     &fence->i915->drm.struct_mutex);
+	if (ret)
+		return ret;
+
 	if (vma) {
 		if (!i915_vma_is_map_and_fenceable(vma))
 			return -EINVAL;
 
-		if (WARN(!i915_gem_object_get_stride(vma->obj) ||
-			 !i915_gem_object_get_tiling(vma->obj),
-			 "bogus fence setup with stride: 0x%x, tiling mode: %i\n",
-			 i915_gem_object_get_stride(vma->obj),
-			 i915_gem_object_get_tiling(vma->obj)))
-			return -EINVAL;
-
 		ret = i915_gem_active_retire(&vma->last_fence,
 					     &vma->obj->base.dev->struct_mutex);
 		if (ret)
@@ -253,7 +304,7 @@ static int fence_update(struct drm_i915_fence_reg *fence,
 	 * to the runtime resume, see i915_gem_restore_fences().
 	 */
 	if (intel_runtime_pm_get_if_in_use(fence->i915)) {
-		fence_write(fence, vma);
+		fence_write(fence, vma, NULL);
 		intel_runtime_pm_put(fence->i915);
 	}
 
@@ -287,7 +338,9 @@ int i915_vma_put_fence(struct i915_vma *vma)
 	if (!fence)
 		return 0;
 
-	if (fence->pin_count)
+	GEM_BUG_ON(fence->vma != vma);
+
+	if (atomic_read(&fence->pin_count))
 		return -EBUSY;
 
 	return fence_update(fence, NULL);
@@ -300,7 +353,7 @@ static struct drm_i915_fence_reg *fence_find(struct drm_i915_private *dev_priv)
 	list_for_each_entry(fence, &dev_priv->mm.fence_list, link) {
 		GEM_BUG_ON(fence->vma && fence->vma->fence != fence);
 
-		if (fence->pin_count)
+		if (atomic_read(&fence->pin_count))
 			continue;
 
 		return fence;
@@ -344,11 +397,16 @@ i915_vma_pin_fence(struct i915_vma *vma)
 	assert_rpm_wakelock_held(vma->vm->i915);
 
 	/* Just update our place in the LRU if our fence is getting reused. */
-	if (vma->fence) {
-		fence = vma->fence;
+	fence = vma->fence;
+	if (fence) {
 		GEM_BUG_ON(fence->vma != vma);
-		fence->pin_count++;
+		atomic_inc(&fence->pin_count);
 		if (!fence->dirty) {
+			err = i915_gem_active_retire(&fence->pipelined,
+						     &fence->i915->drm.struct_mutex);
+			if (err)
+				goto out_unpin;
+
 			list_move_tail(&fence->link,
 				       &fence->i915->mm.fence_list);
 			return 0;
@@ -358,8 +416,8 @@ i915_vma_pin_fence(struct i915_vma *vma)
 		if (IS_ERR(fence))
 			return PTR_ERR(fence);
 
-		GEM_BUG_ON(fence->pin_count);
-		fence->pin_count++;
+		GEM_BUG_ON(atomic_read(&fence->pin_count));
+		atomic_inc(&fence->pin_count);
 	} else
 		return 0;
 
@@ -374,10 +432,97 @@ i915_vma_pin_fence(struct i915_vma *vma)
 		return 0;
 
 out_unpin:
-	fence->pin_count--;
+	atomic_dec(&fence->pin_count);
 	return err;
 }
 
+int i915_vma_reserve_fence(struct i915_vma *vma)
+{
+	struct drm_i915_fence_reg *fence;
+
+	lockdep_assert_held(&vma->vm->i915->drm.struct_mutex);
+	GEM_BUG_ON(!drm_mm_node_allocated(&vma->node));
+	GEM_BUG_ON(!i915_vma_is_pinned(vma));
+
+	fence = vma->fence;
+	if (!fence) {
+		if (!i915_gem_object_is_tiled(vma->obj))
+			return 0;
+
+		if (!i915_vma_is_map_and_fenceable(vma))
+			return -EINVAL;
+
+		fence = fence_find(vma->vm->i915);
+		if (IS_ERR(fence))
+			return PTR_ERR(fence);
+
+		vma->fence = fence;
+
+		if (fence->vma) {
+			i915_gem_release_mmap(fence->vma->obj);
+			fence->vma->fence = NULL;
+		}
+		fence->vma = vma;
+		fence->dirty = true;
+	}
+	atomic_inc(&fence->pin_count);
+	list_move_tail(&fence->link, &fence->i915->mm.fence_list);
+
+	GEM_BUG_ON(!i915_gem_object_is_tiled(vma->obj));
+	GEM_BUG_ON(!i915_vma_is_map_and_fenceable(vma));
+	GEM_BUG_ON(vma->node.size != vma->fence_size);
+	GEM_BUG_ON(!IS_ALIGNED(vma->node.start, vma->fence_alignment));
+
+	return 0;
+}
+
+int i915_vma_emit_pipelined_fence(struct i915_vma *vma,
+				  struct drm_i915_gem_request *rq)
+{
+	struct drm_i915_fence_reg *fence = vma->fence;
+	struct drm_i915_gem_request *prev;
+	int err;
+
+	lockdep_assert_held(&vma->vm->i915->drm.struct_mutex);
+	GEM_BUG_ON(fence && !atomic_read(&fence->pin_count));
+
+	if (!fence)
+		goto out;
+
+	prev = i915_gem_active_raw(&fence->pipelined,
+				   &fence->i915->drm.struct_mutex);
+	if (prev) {
+		err = i915_gem_request_await_dma_fence(rq, &prev->fence);
+		if (err)
+			return err;
+	}
+
+	if (!fence->dirty)
+		goto out;
+
+	GEM_BUG_ON(!i915_vma_is_map_and_fenceable(vma));
+
+	if (fence->vma) {
+		prev = i915_gem_active_raw(&fence->vma->last_fence,
+					   &fence->i915->drm.struct_mutex);
+		if (prev) {
+			err = i915_gem_request_await_dma_fence(rq,
+							       &prev->fence);
+			if (err)
+				return err;
+		}
+	}
+
+	err = fence_write(fence, vma, rq);
+	if (err)
+		return err;
+
+	i915_gem_active_set(&fence->pipelined, rq);
+out:
+	i915_gem_active_set(&vma->last_fence, rq);
+	return 0;
+}
+
 /**
  * i915_gem_revoke_fences - revoke fence state
  * @dev_priv: i915 device private
@@ -428,6 +573,7 @@ void i915_gem_restore_fences(struct drm_i915_private *dev_priv)
 		 */
 		if (vma && !i915_gem_object_is_tiled(vma->obj)) {
 			GEM_BUG_ON(!reg->dirty);
+			GEM_BUG_ON(atomic_read(&reg->pin_count));
 			GEM_BUG_ON(!list_empty(&vma->obj->userfault_link));
 
 			list_move(&reg->link, &dev_priv->mm.fence_list);
@@ -435,7 +581,7 @@ void i915_gem_restore_fences(struct drm_i915_private *dev_priv)
 			vma = NULL;
 		}
 
-		fence_write(reg, vma);
+		fence_write(reg, vma, NULL);
 		reg->vma = vma;
 	}
 }
diff --git a/drivers/gpu/drm/i915/i915_gem_fence_reg.h b/drivers/gpu/drm/i915/i915_gem_fence_reg.h
index 99a31ded4dfd..f69d894997fb 100644
--- a/drivers/gpu/drm/i915/i915_gem_fence_reg.h
+++ b/drivers/gpu/drm/i915/i915_gem_fence_reg.h
@@ -36,7 +36,7 @@ struct drm_i915_fence_reg {
 	struct list_head link;
 	struct drm_i915_private *i915;
 	struct i915_vma *vma;
-	int pin_count;
+	atomic_t pin_count;
 	int id;
 	/**
 	 * Whether the tiling parameters for the currently
@@ -47,6 +47,7 @@ struct drm_i915_fence_reg {
 	 * command (such as BLT on gen2/3), as a "fence".
 	 */
 	bool dirty;
+	struct i915_gem_active pipelined;
 };
 
 #endif
diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index 826d5ea48fbb..205b9b3b4e1c 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -714,6 +714,7 @@ int i915_vma_unbind(struct i915_vma *vma)
 		__i915_vma_iounmap(vma);
 		vma->flags &= ~I915_VMA_CAN_FENCE;
 	}
+	GEM_BUG_ON(vma->fence);
 
 	if (likely(!vma->vm->closed)) {
 		trace_i915_vma_unbind(vma);
diff --git a/drivers/gpu/drm/i915/i915_vma.h b/drivers/gpu/drm/i915/i915_vma.h
index ab4a3c0b1526..1c0f9def81ab 100644
--- a/drivers/gpu/drm/i915/i915_vma.h
+++ b/drivers/gpu/drm/i915/i915_vma.h
@@ -349,8 +349,8 @@ int __must_check i915_vma_put_fence(struct i915_vma *vma);
 
 static inline void __i915_vma_unpin_fence(struct i915_vma *vma)
 {
-	GEM_BUG_ON(vma->fence->pin_count <= 0);
-	vma->fence->pin_count--;
+	GEM_BUG_ON(atomic_read(&vma->fence->pin_count) <= 0);
+	atomic_dec(&vma->fence->pin_count);
 }
 
 /**
@@ -364,10 +364,17 @@ static inline void __i915_vma_unpin_fence(struct i915_vma *vma)
 static inline void
 i915_vma_unpin_fence(struct i915_vma *vma)
 {
-	lockdep_assert_held(&vma->obj->base.dev->struct_mutex);
+	/* The assumption is if the caller has a fence, the caller owns a pin
+	 * on that fence, i.e. that vma->fence cannot become NULL prior to us
+	 * releasing our pin.
+	 */
 	if (vma->fence)
 		__i915_vma_unpin_fence(vma);
 }
 
+int __must_check i915_vma_reserve_fence(struct i915_vma *vma);
+int i915_vma_emit_pipelined_fence(struct i915_vma *vma,
+				  struct drm_i915_gem_request *rq);
+
 #endif
 
-- 
2.14.1



More information about the Intel-gfx-trybot mailing list