[PATCH v2] drm/i915: Pre-allocation of shmem pages of a GEM object

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From: Akash Goel <akash.goel@xxxxxxxxx>

This patch could help to reduce the time, 'struct_mutex' is kept
locked during either the exec-buffer path or Page fault
handling path as now the backing pages are requested from shmem layer
without holding the 'struct_mutex'.

v2: Fixed the merge issue, due to which 'exec_lock' mutex was not released.

Signed-off-by: Akash Goel <akash.goel@xxxxxxxxx>
---
 drivers/gpu/drm/i915/i915_debugfs.c        |  9 +++-
 drivers/gpu/drm/i915/i915_dma.c            |  1 +
 drivers/gpu/drm/i915/i915_drv.h            |  5 ++
 drivers/gpu/drm/i915/i915_gem.c            | 75 ++++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 87 ++++++++++++++++++++++++++----
 drivers/gpu/drm/i915/i915_trace.h          | 35 ++++++++++++
 6 files changed, 200 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 18b3565..70c752b 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -247,10 +247,16 @@ static int i915_gem_stolen_list_info(struct seq_file *m, void *data)
 	LIST_HEAD(stolen);
 	int count, ret;
 
-	ret = mutex_lock_interruptible(&dev->struct_mutex);
+	ret = mutex_lock_interruptible(&dev_priv->exec_lock);
 	if (ret)
 		return ret;
 
+	ret = mutex_lock_interruptible(&dev->struct_mutex);
+	if (ret) {
+		mutex_unlock(&dev_priv->exec_lock);
+		return ret;
+	}
+
 	total_obj_size = total_gtt_size = count = 0;
 	list_for_each_entry(obj, &dev_priv->mm.bound_list, global_list) {
 		if (obj->stolen == NULL)
@@ -281,6 +287,7 @@ static int i915_gem_stolen_list_info(struct seq_file *m, void *data)
 		list_del_init(&obj->obj_exec_link);
 	}
 	mutex_unlock(&dev->struct_mutex);
+	mutex_unlock(&dev_priv->exec_lock);
 
 	seq_printf(m, "Total %d objects, %zu bytes, %zu GTT size\n",
 		   count, total_obj_size, total_gtt_size);
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index e393a14..e4d1cb0 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1572,6 +1572,7 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 	dev_priv->ring_index = 0;
 	mutex_init(&dev_priv->dpio_lock);
 	mutex_init(&dev_priv->modeset_restore_lock);
+	mutex_init(&dev_priv->exec_lock);
 
 	intel_pm_setup(dev);
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 5f4f631..6dc579a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1475,6 +1475,8 @@ struct drm_i915_private {
 	struct i915_ums_state ums;
 	/* the indicator for dispatch video commands on two BSD rings */
 	int ring_index;
+	/* for concurrent execbuffer protection */
+	struct mutex exec_lock;
 };
 
 static inline struct drm_i915_private *to_i915(const struct drm_device *dev)
@@ -2116,6 +2118,9 @@ int i915_gem_dumb_create(struct drm_file *file_priv,
 			 struct drm_mode_create_dumb *args);
 int i915_gem_mmap_gtt(struct drm_file *file_priv, struct drm_device *dev,
 		      uint32_t handle, uint64_t *offset);
+void
+i915_gem_object_shmem_preallocate(struct drm_i915_gem_object *obj);
+
 /**
  * Returns true if seq1 is later than seq2.
  */
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index dae51c3..b19ccb8 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1408,6 +1408,8 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	page_offset = ((unsigned long)vmf->virtual_address - vma->vm_start) >>
 		PAGE_SHIFT;
 
+	i915_gem_object_shmem_preallocate(obj);
+
 	ret = i915_mutex_lock_interruptible(dev);
 	if (ret)
 		goto out;
@@ -1873,6 +1875,79 @@ i915_gem_shrink_all(struct drm_i915_private *dev_priv)
 	return __i915_gem_shrink(dev_priv, LONG_MAX, false);
 }
 
+void
+i915_gem_object_shmem_preallocate(struct drm_i915_gem_object *obj)
+{
+	int page_count, i;
+	struct address_space *mapping;
+	struct page *page;
+	gfp_t gfp;
+
+	if (obj->pages)
+		return;
+
+	if (obj->madv != I915_MADV_WILLNEED) {
+		DRM_ERROR("Attempting to preallocate a purgeable object\n");
+		return;
+	}
+
+	if (obj->base.filp) {
+		int ret;
+		struct inode *inode = file_inode(obj->base.filp);
+		struct shmem_inode_info *info = SHMEM_I(inode);
+		if (!inode)
+			return;
+		/* The alloced field stores how many data pages are allocated
+		 * to the file. If already shmem space has been allocated for
+		 * the object, then we can simply return */
+		spin_lock(&info->lock);
+		ret = info->alloced;
+		spin_unlock(&info->lock);
+		if (ret > 0) {
+			DRM_DEBUG_DRIVER("Already shmem space alloced for obj %p, %d pages\n",
+					obj, ret);
+			return;
+		}
+	} else
+		return;
+
+	BUG_ON(obj->pages_pin_count);
+
+	/* Assert that the object is not currently in any GPU domain. As it
+	 * wasn't in the GTT, there shouldn't be any way it could have been in
+	 * a GPU cache
+	 */
+	BUG_ON(obj->base.read_domains & I915_GEM_GPU_DOMAINS);
+	BUG_ON(obj->base.write_domain & I915_GEM_GPU_DOMAINS);
+
+	trace_i915_gem_obj_prealloc_start(obj, obj->base.size);
+
+	page_count = obj->base.size / PAGE_SIZE;
+
+	/* Get the list of pages out of our struct file
+	 * Fail silently without starting the shrinker
+	 */
+	mapping = file_inode(obj->base.filp)->i_mapping;
+	gfp = mapping_gfp_mask(mapping);
+	gfp |= __GFP_NORETRY | __GFP_NOWARN | __GFP_NO_KSWAPD;
+	gfp &= ~(__GFP_IO | __GFP_WAIT);
+	for (i = 0; i < page_count; i++) {
+		page = shmem_read_mapping_page_gfp(mapping, i, gfp);
+		if (IS_ERR(page)) {
+			DRM_DEBUG_DRIVER("Failure for obj(%p), size(%x) at page(%d)\n",
+						obj, obj->base.size, i);
+			break;
+		}
+		/* Decrement the extra ref count on the returned page,
+		   otherwise when 'get_pages_gtt' will be called later on
+		   in the regular path, it will also increment the ref count,
+		   which will disturb the ref count management */
+		page_cache_release(page);
+	}
+
+	trace_i915_gem_obj_prealloc_end(obj);
+}
+
 static int
 i915_gem_object_get_pages_gtt(struct drm_i915_gem_object *obj)
 {
diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 6cc004f..da3cbdc 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -38,6 +38,7 @@
 
 struct eb_vmas {
 	struct list_head vmas;
+	struct list_head objects;
 	int and;
 	union {
 		struct i915_vma *lut[0];
@@ -93,10 +94,9 @@ eb_lookup_vmas(struct eb_vmas *eb,
 {
 	struct drm_i915_private *dev_priv = vm->dev->dev_private;
 	struct drm_i915_gem_object *obj;
-	struct list_head objects;
 	int i, ret;
 
-	INIT_LIST_HEAD(&objects);
+	INIT_LIST_HEAD(&eb->objects);
 	spin_lock(&file->table_lock);
 	/* Grab a reference to the object and release the lock so we can lookup
 	 * or create the VMA without using GFP_ATOMIC */
@@ -119,12 +119,12 @@ eb_lookup_vmas(struct eb_vmas *eb,
 		}
 
 		drm_gem_object_reference(&obj->base);
-		list_add_tail(&obj->obj_exec_link, &objects);
+		list_add_tail(&obj->obj_exec_link, &eb->objects);
 	}
 	spin_unlock(&file->table_lock);
 
 	i = 0;
-	while (!list_empty(&objects)) {
+	while (!list_empty(&eb->objects)) {
 		struct i915_vma *vma;
 		struct i915_address_space *bind_vm = vm;
 
@@ -141,7 +141,7 @@ eb_lookup_vmas(struct eb_vmas *eb,
 		    (i == (args->buffer_count - 1))))
 			bind_vm = &dev_priv->gtt.base;
 
-		obj = list_first_entry(&objects,
+		obj = list_first_entry(&eb->objects,
 				       struct drm_i915_gem_object,
 				       obj_exec_link);
 
@@ -162,7 +162,6 @@ eb_lookup_vmas(struct eb_vmas *eb,
 
 		/* Transfer ownership from the objects list to the vmas list. */
 		list_add_tail(&vma->exec_list, &eb->vmas);
-		list_del_init(&obj->obj_exec_link);
 
 		vma->exec_entry = &exec[i];
 		if (eb->and < 0) {
@@ -180,8 +179,8 @@ eb_lookup_vmas(struct eb_vmas *eb,
 
 
 err:
-	while (!list_empty(&objects)) {
-		obj = list_first_entry(&objects,
+	while (!list_empty(&eb->objects)) {
+		obj = list_first_entry(&eb->objects,
 				       struct drm_i915_gem_object,
 				       obj_exec_link);
 		list_del_init(&obj->obj_exec_link);
@@ -249,6 +248,15 @@ static void eb_destroy(struct eb_vmas *eb)
 		i915_gem_execbuffer_unreserve_vma(vma);
 		drm_gem_object_unreference(&vma->obj->base);
 	}
+
+	while (!list_empty(&eb->objects)) {
+		struct drm_i915_gem_object *obj;
+		obj = list_first_entry(&eb->objects,
+				struct drm_i915_gem_object,
+				obj_exec_link);
+		list_del_init(&obj->obj_exec_link);
+	}
+
 	kfree(eb);
 }
 
@@ -712,6 +720,7 @@ i915_gem_execbuffer_relocate_slow(struct drm_device *dev,
 				  struct eb_vmas *eb,
 				  struct drm_i915_gem_exec_object2 *exec)
 {
+	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_gem_relocation_entry *reloc;
 	struct i915_address_space *vm;
 	struct i915_vma *vma;
@@ -786,12 +795,24 @@ i915_gem_execbuffer_relocate_slow(struct drm_device *dev,
 		total += exec[i].relocation_count;
 	}
 
+	/* First acquire the 'exec_lock' mutex to prevent the concurrent
+	 * access to the 'obj_exec_link' field of the objects, by the
+	 * preallocation routine from the context of a new execbuffer ioctl */
+	ret = mutex_lock_interruptible(&dev_priv->exec_lock);
+	if (ret) {
+		mutex_lock(&dev->struct_mutex);
+		goto err;
+	}
+
 	ret = i915_mutex_lock_interruptible(dev);
 	if (ret) {
 		mutex_lock(&dev->struct_mutex);
 		goto err;
 	}
 
+	/* Now release the 'exec_lock' after acquiring the 'struct mutex' */
+	mutex_unlock(&dev_priv->exec_lock);
+
 	/* reacquire the objects */
 	eb_reset(eb);
 	ret = eb_lookup_vmas(eb, exec, args, vm, file);
@@ -856,6 +877,21 @@ i915_gem_execbuffer_move_to_gpu(struct intel_ring_buffer *ring,
 	return intel_ring_invalidate_all_caches(ring);
 }
 
+static void
+i915_gem_execbuffer_preallocate_objs(struct list_head *objects)
+{
+	struct drm_i915_gem_object *obj;
+
+	/* Try to get the obj pages atomically */
+	while (!list_empty(objects)) {
+		obj = list_first_entry(objects,
+				struct drm_i915_gem_object,
+				obj_exec_link);
+		i915_gem_object_shmem_preallocate(obj);
+		list_del_init(&obj->obj_exec_link);
+	}
+}
+
 static bool
 i915_gem_check_execbuffer(struct drm_i915_gem_execbuffer2 *exec)
 {
@@ -1173,12 +1209,19 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 
 	intel_runtime_pm_get(dev_priv);
 
-	ret = i915_mutex_lock_interruptible(dev);
+	ret = mutex_lock_interruptible(&dev_priv->exec_lock);
 	if (ret)
 		goto pre_mutex_err;
 
+	ret = i915_mutex_lock_interruptible(dev);
+	if (ret) {
+		mutex_unlock(&dev_priv->exec_lock);
+		goto pre_mutex_err;
+	}
+
 	if (dev_priv->ums.mm_suspended) {
 		mutex_unlock(&dev->struct_mutex);
+		mutex_unlock(&dev_priv->exec_lock);
 		ret = -EBUSY;
 		goto pre_mutex_err;
 	}
@@ -1200,14 +1243,36 @@ i915_gem_do_execbuffer(struct drm_device *dev, void *data,
 	if (eb == NULL) {
 		i915_gem_context_unreference(ctx);
 		mutex_unlock(&dev->struct_mutex);
+		mutex_unlock(&dev_priv->exec_lock);
 		ret = -ENOMEM;
 		goto pre_mutex_err;
 	}
 
 	/* Look up object handles */
 	ret = eb_lookup_vmas(eb, exec, args, vm, file);
-	if (ret)
-		goto err;
+	if (ret) {
+		eb_destroy(eb);
+		i915_gem_context_unreference(ctx);
+		mutex_unlock(&dev->struct_mutex);
+		mutex_unlock(&dev_priv->exec_lock);
+		goto pre_mutex_err;
+	}
+
+	/*
+	 * Release the 'struct_mutex' before extracting the backing
+	 * pages of the objects, so as to allow other ioctls to get serviced,
+	 * while backing pages are being allocated (which is generally
+	 * the most time consuming phase). The 'exec_lock' mutex will provide
+	 * the protection meanwhile.
+	 */
+	mutex_unlock(&dev->struct_mutex);
+
+	i915_gem_execbuffer_preallocate_objs(&eb->objects);
+
+	/* Reacquire the 'struct_mutex' post preallocation */
+	ret = i915_mutex_lock_interruptible(dev);
+
+	mutex_unlock(&dev_priv->exec_lock);
 
 	/* take note of the batch buffer before we might reorder the lists */
 	batch_obj = list_entry(eb->vmas.prev, struct i915_vma, exec_list)->obj;
diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
index b29d7b1..21bf10d 100644
--- a/drivers/gpu/drm/i915/i915_trace.h
+++ b/drivers/gpu/drm/i915/i915_trace.h
@@ -245,6 +245,41 @@ TRACE_EVENT(i915_gem_object_fault,
 		      __entry->write ? ", writable" : "")
 );
 
+TRACE_EVENT(i915_gem_obj_prealloc_start,
+	    TP_PROTO(struct drm_i915_gem_object *obj, u32 size),
+	    TP_ARGS(obj, size),
+
+	    TP_STRUCT__entry(
+			     __field(struct drm_i915_gem_object *, obj)
+			     __field(u32, size)
+			     ),
+
+	    TP_fast_assign(
+			   __entry->obj = obj;
+			   __entry->size = size;
+			   ),
+
+	    TP_printk("obj=%p, size=%x",
+		      __entry->obj,
+		      __entry->size)
+);
+
+TRACE_EVENT(i915_gem_obj_prealloc_end,
+	    TP_PROTO(struct drm_i915_gem_object *obj),
+	    TP_ARGS(obj),
+
+	    TP_STRUCT__entry(
+			     __field(struct drm_i915_gem_object *, obj)
+			     ),
+
+	    TP_fast_assign(
+			   __entry->obj = obj;
+			   ),
+
+	    TP_printk("obj=%p",
+		      __entry->obj)
+);
+
 DECLARE_EVENT_CLASS(i915_gem_object,
 	    TP_PROTO(struct drm_i915_gem_object *obj),
 	    TP_ARGS(obj),
-- 
1.9.2

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