Re: [PATCH v3 3/6] drm/i915 Implement LMEM backup and restore for suspend / resume

On 14/09/2021 20:31, Thomas Hellström wrote:

Just evict unpinned objects to system. For pinned LMEM objects, make a backup system object and blit the contents to that.

Backup is performed in three steps, 1: Opportunistically evict evictable objects using the gpu blitter. 2: After gt idle, evict evictable objects using the gpu blitter. This will be modified in an upcoming patch to backup pinned objects that are not used by the blitter itself. 3: Backup remaining pinned objects using memcpy.

Also move uC suspend to after 2) to make sure we have a functional GuC during 2) if using GuC submission.

v2:

• Major refactor to make sure gem_exec_suspend@hang-SX subtests work, and suspend / resume works with a slightly modified GuC submission enabling patch series.

v3:

• Fix a potential use-after-free (Matthew Auld)
• Use i915_gem_object_create_shmem() instead of i915_gem_object_create_region (Matthew Auld)
• Minor simplifications (Matthew Auld)
• Fix up kerneldoc for i195_ttm_restore_region().
• Final lmem_suspend() call moved to i915_gem_backup_suspend from i915_gem_suspend_late, since the latter gets called at driver unload and we don't unnecessarily want to run it at that time.

Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com

<snip>

+static int i915_ttm_restore(struct i915_gem_apply_to_region *apply,

• 	    struct drm_i915_gem_object *obj)
  

+{

• struct i915_gem_ttm_pm_apply *pm_apply =

• container_of(apply, typeof(*pm_apply), base);
  

• struct drm_i915_gem_object *backup = obj->ttm.backup;
• struct ttm_buffer_object *backup_bo = i915_gem_to_ttm(backup);
• struct ttm_operation_ctx ctx = {};
• int err;
• if (!backup)

• return 0;
  

• if (!pm_apply->allow_gpu && (obj->flags & I915_BO_ALLOC_USER))

• return 0;
  

Hmm, do we ever hit this? I would presume anything that userspace directly allocated in lmem can be kicked out with ttm_bo_validate(sys) i.e backup == NULL?

• err = i915_gem_object_lock(backup, apply->ww);
• if (err)

• return err;
  

• /* Content may have been swapped. */
• err = ttm_tt_populate(backup_bo->bdev, backup_bo->ttm, &ctx);
• if (!err) {

• err = i915_gem_obj_copy_ttm(obj, backup, pm_apply->allow_gpu,
  

• 			    false);
  

• GEM_WARN_ON(err);
  

• obj->ttm.backup = NULL;
  

• err = 0;
  

• }
• i915_gem_ww_unlock_single(backup);
• if (!err)

• i915_gem_object_put(backup);
  

• return err;

+}