drm/vram: Implement lazy unmapping for GEM VRAM buffers

Frequent mapping and unmapping a buffer object adds overhead for
modifying the page table and creates debug output. Unmapping a buffer
is only required when the memory manager evicts the buffer from its
current location.

v4:
	* WARN_ON if buffer is still mapped during BO cleanup

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reported-and-tested-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20190906122056.32018-5-tzimmermann@suse.de

diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
index 1e17f11cc7b9f1641f6d090f86a00456ba75e407..0990f0e032133e54598fedfca9bf2c84991cf3b6 100644 (file)
--- a/drivers/gpu/drm/drm_gem_vram_helper.c
+++ b/drivers/gpu/drm/drm_gem_vram_helper.c
@@ -28,6 +28,7 @@ static void drm_gem_vram_cleanup(struct drm_gem_vram_object *gbo)
         */
 
        WARN_ON(gbo->kmap_use_count);
+       WARN_ON(gbo->kmap.virtual);
 
        drm_gem_object_release(&gbo->bo.base);
 }
@@ -356,18 +357,17 @@ EXPORT_SYMBOL(drm_gem_vram_kmap);
 
 static void drm_gem_vram_kunmap_locked(struct drm_gem_vram_object *gbo)
 {
-       struct ttm_bo_kmap_obj *kmap = &gbo->kmap;
-
        if (WARN_ON_ONCE(!gbo->kmap_use_count))
                return;
        if (--gbo->kmap_use_count > 0)
                return;
 
-       if (!kmap->virtual)
-               return;
-
-       ttm_bo_kunmap(kmap);
-       kmap->virtual = NULL;
+       /*
+        * Permanently mapping and unmapping buffers adds overhead from
+        * updating the page tables and creates debugging output. Therefore,
+        * we delay the actual unmap operation until the BO gets evicted
+        * from memory. See drm_gem_vram_bo_driver_move_notify().
+        */
 }
 
 /**
@@ -497,6 +497,38 @@ int drm_gem_vram_bo_driver_verify_access(struct ttm_buffer_object *bo,
 }
 EXPORT_SYMBOL(drm_gem_vram_bo_driver_verify_access);
 
+/**
+ * drm_gem_vram_bo_driver_move_notify() -
+ *     Implements &struct ttm_bo_driver.move_notify
+ * @bo:                TTM buffer object. Refers to &struct drm_gem_vram_object.bo
+ * @evict:     True, if the BO is being evicted from graphics memory;
+ *             false otherwise.
+ * @new_mem:   New memory region, or NULL on destruction
+ */
+void drm_gem_vram_bo_driver_move_notify(struct ttm_buffer_object *bo,
+                                       bool evict,
+                                       struct ttm_mem_reg *new_mem)
+{
+       struct drm_gem_vram_object *gbo;
+       struct ttm_bo_kmap_obj *kmap;
+
+       /* TTM may pass BOs that are not GEM VRAM BOs. */
+       if (!drm_is_gem_vram(bo))
+               return;
+
+       gbo = drm_gem_vram_of_bo(bo);
+       kmap = &gbo->kmap;
+
+       if (WARN_ON_ONCE(gbo->kmap_use_count))
+               return;
+
+       if (!kmap->virtual)
+               return;
+       ttm_bo_kunmap(kmap);
+       kmap->virtual = NULL;
+}
+EXPORT_SYMBOL(drm_gem_vram_bo_driver_move_notify);
+
 /*
  * drm_gem_vram_mm_funcs - Functions for &struct drm_vram_mm
  *
@@ -506,7 +538,8 @@ EXPORT_SYMBOL(drm_gem_vram_bo_driver_verify_access);
  */
 const struct drm_vram_mm_funcs drm_gem_vram_mm_funcs = {
        .evict_flags = drm_gem_vram_bo_driver_evict_flags,
-       .verify_access = drm_gem_vram_bo_driver_verify_access
+       .verify_access = drm_gem_vram_bo_driver_verify_access,
+       .move_notify = drm_gem_vram_bo_driver_move_notify,
 };
 EXPORT_SYMBOL(drm_gem_vram_mm_funcs);
 

diff --git a/include/drm/drm_gem_vram_helper.h b/include/drm/drm_gem_vram_helper.h
index 4f0e207ee097e0a3217b31fdd12b183917a771d5..b47c46516466ac34b4f9dce828937119e495991c 100644 (file)
--- a/include/drm/drm_gem_vram_helper.h
+++ b/include/drm/drm_gem_vram_helper.h
@@ -112,6 +112,10 @@ int drm_gem_vram_fill_create_dumb(struct drm_file *file,
 void drm_gem_vram_bo_driver_evict_flags(struct ttm_buffer_object *bo,
                                        struct ttm_placement *pl);
 
+void drm_gem_vram_bo_driver_move_notify(struct ttm_buffer_object *bo,
+                                       bool evict,
+                                       struct ttm_mem_reg *new_mem);
+
 int drm_gem_vram_bo_driver_verify_access(struct ttm_buffer_object *bo,
                                         struct file *filp);