RE: [PATCH v3 1/5] drm/i915/gem: Implement object migration

-----Original Message----- From: dri-devel dri-devel-bounces@lists.freedesktop.org On Behalf Of Thomas Hellström Sent: Monday, June 28, 2021 10:46 AM To: intel-gfx@lists.freedesktop.org; dri-devel@lists.freedesktop.org Cc: Thomas Hellström thomas.hellstrom@linux.intel.com; Auld, Matthew matthew.auld@intel.com; lkp lkp@intel.com Subject: [PATCH v3 1/5] drm/i915/gem: Implement object migration

Introduce an interface to migrate objects between regions. This is primarily intended to migrate objects to LMEM for display and to SYSTEM for dma-buf, but might be reused in one form or another for performance-based migration.

v2:

• Verify that the memory region given as an id really exists.

(Reported by Matthew Auld)

• Call i915_gem_object_{init,release}_memory_region() when switching

region to handle also switching region lists. (Reported by Matthew Auld) v3:

• Fix i915_gem_object_can_migrate() to return true if object is already in

the correct region, even if the object ops doesn't have a migrate() callback.

• Update typo in commit message.
• Fix kerneldoc of i915_gem_object_wait_migration().

Reported-by: kernel test robot lkp@intel.com Signed-off-by: Thomas Hellström thomas.hellstrom@linux.intel.com

---

drivers/gpu/drm/i915/gem/i915_gem_object.c | 96 +++++++++++++++++++ drivers/gpu/drm/i915/gem/i915_gem_object.h | 12 +++ .../gpu/drm/i915/gem/i915_gem_object_types.h | 9 ++ drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 69 +++++++++---- drivers/gpu/drm/i915/gem/i915_gem_wait.c | 19 ++++ 5 files changed, 188 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c index 07e8ff9a8aae..1c18be067b58 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c @@ -513,6 +513,102 @@ bool i915_gem_object_has_iomem(const struct drm_i915_gem_object *obj) return obj->mem_flags & I915_BO_FLAG_IOMEM; }

+/**

• • i915_gem_object_can_migrate - Whether an object likely can be migrated
• • @obj: The object to migrate
• • @id: The region intended to migrate to
• • Check whether the object backend supports migration to the
• • given region. Note that pinning may affect the ability to migrate.
• • Return: true if migration is possible, false otherwise.
• */

+bool i915_gem_object_can_migrate(struct drm_i915_gem_object *obj,

• 		 enum intel_region_id id)
  

+{

• struct drm_i915_private *i915 = to_i915(obj->base.dev);
• unsigned int num_allowed = obj->mm.n_placements;
• struct intel_memory_region *mr;
• unsigned int i;
• GEM_BUG_ON(id >= INTEL_REGION_UNKNOWN);
• GEM_BUG_ON(obj->mm.madv != I915_MADV_WILLNEED);
• mr = i915->mm.regions[id];
• if (!mr)

• return false;
  

• if (obj->mm.region == mr)

• return true;
  

• if (!i915_gem_object_evictable(obj))

• return false;
  

• if (!obj->ops->migrate)

• return false;
  

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

• return true;
  

• if (num_allowed == 0)

• return false;
  

• for (i = 0; i < num_allowed; ++i) {

• if (mr == obj->mm.placements[i])
  

• 	return true;
  

• }

Hi Thomas,

I am a little confused over the difference in checks between this function and i915_gem_object_migrate().

Why is the lack of an mr a BUG_ON in _object_migrate(), but here it just false?

So that means that under certain circumstances, you could not have a mr?

If that is the case, when?

Would that be when the I915_BO_ALLOC_USER is set?

If so, should there be a check for "non" user vs user?

Or maybe document this function pointing out why there are differences and why?

• return false;

+}

+/**

• • i915_gem_object_migrate - Migrate an object to the desired region id
• • @obj: The object to migrate.
• • @ww: An optional struct i915_gem_ww_ctx. If NULL, the backend may
• • not be successful in evicting other objects to make room for this object.

Is the ww for future consideration? (I don't see any use of it in the patch).

• • @id: The region id to migrate to.
• • Attempt to migrate the object to the desired memory region. The
• • object backend must support migration and the object may not be
• • pinned, (explicitly pinned pages or pinned vmas). The object must
• • be locked.
• • On successful completion, the object will have pages pointing to
• • memory in the new region, but an async migration task may not have
• • completed yet, and to accomplish that,

i915_gem_object_wait_migration()

• • must be called.
• • Return: 0 on success. Negative error code on failure. In particular may
• • return -ENXIO on lack of region space, -EDEADLK for deadlock avoidance
• • if @ww is set, -EINTR or -ERESTARTSYS if signal pending, and
• • -EBUSY if the object is pinned.
• */

+int i915_gem_object_migrate(struct drm_i915_gem_object *obj,

• 	    struct i915_gem_ww_ctx *ww,
  

• 	    enum intel_region_id id)
  

+{

• struct drm_i915_private *i915 = to_i915(obj->base.dev);
• struct intel_memory_region *mr;
• GEM_BUG_ON(id >= INTEL_REGION_UNKNOWN);
• GEM_BUG_ON(obj->mm.madv != I915_MADV_WILLNEED);
• assert_object_held(obj);
• mr = i915->mm.regions[id];
• GEM_BUG_ON(!mr);
• if (obj->mm.region == mr)

• return 0;
  

• if (!i915_gem_object_evictable(obj))

• return -EBUSY;
  

• if (!obj->ops->migrate)

• return -EOPNOTSUPP;
  

Why aren't you using _can_migrate here?

• return obj->ops->migrate(obj, mr);

+}

void i915_gem_init__objects(struct drm_i915_private *i915) { INIT_WORK(&i915->mm.free_work, __i915_gem_free_work); diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h index ea3224a480c4..8cbd7a5334e2 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h @@ -17,6 +17,8 @@ #include "i915_gem_ww.h" #include "i915_vma_types.h"

+enum intel_region_id;

/*

• XXX: There is a prevalence of the assumption that we fit the
• object's page count inside a 32bit _signed_ variable. Let's document

@@ -597,6 +599,16 @@ bool i915_gem_object_migratable(struct drm_i915_gem_object *obj);

bool i915_gem_object_validates_to_lmem(struct drm_i915_gem_object *obj);

+int i915_gem_object_migrate(struct drm_i915_gem_object *obj,

• 	    struct i915_gem_ww_ctx *ww,
  

• 	    enum intel_region_id id);
  

+bool i915_gem_object_can_migrate(struct drm_i915_gem_object *obj,

• 		 enum intel_region_id id);
  

+int i915_gem_object_wait_migration(struct drm_i915_gem_object *obj,

• 		   unsigned int flags);
  

#ifdef CONFIG_MMU_NOTIFIER static inline bool i915_gem_object_is_userptr(struct drm_i915_gem_object *obj) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h index 441f913c87e6..ef3de2ae9723 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h @@ -18,6 +18,7 @@

struct drm_i915_gem_object; struct intel_fronbuffer; +struct intel_memory_region;

/*

• struct i915_lut_handle tracks the fast lookups from handle to vma used

@@ -77,6 +78,14 @@ struct drm_i915_gem_object_ops { * delayed_free - Override the default delayed free implementation */ void (*delayed_free)(struct drm_i915_gem_object *obj);

• /**

• * migrate - Migrate object to a different region either for
  

• * pinning or for as long as the object lock is held.
  

• */
  

• int (*migrate)(struct drm_i915_gem_object *obj,

•        struct intel_memory_region *mr);
  

• void (*release)(struct drm_i915_gem_object *obj);

  const struct vm_operations_struct *mmap_ops;

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c index c39d982c4fa6..8f89185b6507 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c @@ -617,7 +617,8 @@ struct ttm_device_funcs *i915_ttm_driver(void) return &i915_ttm_bo_driver; }

-static int i915_ttm_get_pages(struct drm_i915_gem_object *obj) +static int __i915_ttm_get_pages(struct drm_i915_gem_object *obj,

• 		struct ttm_placement *placement)
  

{ struct ttm_buffer_object *bo = i915_gem_to_ttm(obj); struct ttm_operation_ctx ctx = { @@ -625,19 +626,12 @@ static int i915_ttm_get_pages(struct drm_i915_gem_object *obj) .no_wait_gpu = false, }; struct sg_table *st;

• struct ttm_place requested, busy[I915_TTM_MAX_PLACEMENTS];

• struct ttm_placement placement; int real_num_busy; int ret;

• GEM_BUG_ON(obj->mm.n_placements >

I915_TTM_MAX_PLACEMENTS);

• /* Move to the requested placement. */
• i915_ttm_placement_from_obj(obj, &requested, busy, &placement);
• /* First try only the requested placement. No eviction. */
• real_num_busy =

fetch_and_zero(&placement.num_busy_placement);

• ret = ttm_bo_validate(bo, &placement, &ctx);

• real_num_busy = fetch_and_zero(&placement-

...

num_busy_placement);

• ret = ttm_bo_validate(bo, placement, &ctx); if (ret) { ret = i915_ttm_err_to_gem(ret); /*

@@ -652,8 +646,8 @@ static int i915_ttm_get_pages(struct drm_i915_gem_object *obj) * If the initial attempt fails, allow all accepted placements, * evicting if necessary. */

• placement.num_busy_placement = real_num_busy;
  

• ret = ttm_bo_validate(bo, &placement, &ctx);
  

• placement->num_busy_placement = real_num_busy;
  

• ret = ttm_bo_validate(bo, placement, &ctx);
  

  if (ret) return i915_ttm_err_to_gem(ret); }

@@ -668,16 +662,56 @@ static int i915_ttm_get_pages(struct drm_i915_gem_object *obj) i915_ttm_adjust_gem_after_move(obj); }

• /* Object either has a page vector or is an iomem object */
• st = bo->ttm ? i915_ttm_tt_get_st(bo->ttm) : obj->ttm.cached_io_st;
• if (IS_ERR(st))

• return PTR_ERR(st);
  

• if (!obj->mm.pages) {

• /* Object either has a page vector or is an iomem object */
  

• st = bo->ttm ? i915_ttm_tt_get_st(bo->ttm) : obj-
  

...

ttm.cached_io_st;

• if (IS_ERR(st))
  

• 	return PTR_ERR(st);
  
  

• __i915_gem_object_set_pages(obj, st, i915_sg_dma_sizes(st->sgl));

• __i915_gem_object_set_pages(obj, st,
  

i915_sg_dma_sizes(st->sgl));

• }

  return ret;

}

+static int i915_ttm_get_pages(struct drm_i915_gem_object *obj) +{

• struct ttm_place requested, busy[I915_TTM_MAX_PLACEMENTS];
• struct ttm_placement placement;
• GEM_BUG_ON(obj->mm.n_placements >

I915_TTM_MAX_PLACEMENTS);

• /* Move to the requested placement. */
• i915_ttm_placement_from_obj(obj, &requested, busy, &placement);
• return __i915_ttm_get_pages(obj, &placement);

+}

+static int i915_ttm_migrate(struct drm_i915_gem_object *obj,

• 	    struct intel_memory_region *mr)
  

+{

• struct ttm_place requested;
• struct ttm_placement placement;
• int ret;
• i915_ttm_place_from_region(mr, &requested, obj->flags);
• placement.num_placement = 1;
• placement.num_busy_placement = 1;
• placement.placement = &requested;
• placement.busy_placement = &requested;
• ret = __i915_ttm_get_pages(obj, &placement);
• if (ret)

• return ret;
  

• if (obj->mm.region != mr) {

• i915_gem_object_release_memory_region(obj);
  

• i915_gem_object_init_memory_region(obj, mr);
  

• }

Perhaps a minor nit:

Doing this after we have done the _get_pages() just doesn't seem right.

I.e. we do work on the object, and then we init some portion of it.

Do we need to do this incase the migration/placement fails? If so, maybe a comment to that effect?

Thanks,

Mike

• return 0;

+}

static void i915_ttm_put_pages(struct drm_i915_gem_object *obj, struct sg_table *st) { @@ -814,6 +848,7 @@ static const struct drm_i915_gem_object_ops i915_gem_ttm_obj_ops = { .truncate = i915_ttm_purge, .adjust_lru = i915_ttm_adjust_lru, .delayed_free = i915_ttm_delayed_free,

• .migrate = i915_ttm_migrate, .mmap_offset = i915_ttm_mmap_offset, .mmap_ops = &vm_ops_ttm,

}; diff --git a/drivers/gpu/drm/i915/gem/i915_gem_wait.c b/drivers/gpu/drm/i915/gem/i915_gem_wait.c index 1070d3afdce7..f909aaa09d9c 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_wait.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_wait.c @@ -290,3 +290,22 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file) i915_gem_object_put(obj); return ret; }

+/**

• • i915_gem_object_wait_migration - Sync an accelerated migration

operation

• • @obj: The migrating object.
• • @flags: waiting flags. Currently supports only I915_WAIT_INTERRUPTIBLE.
• • Wait for any pending async migration operation on the object,
• • whether it's explicitly (i915_gem_object_migrate()) or implicitly
• • (swapin, initial clearing) initiated.
• • Return: 0 if successful, -ERESTARTSYS if a signal was hit during waiting.
• */

+int i915_gem_object_wait_migration(struct drm_i915_gem_object *obj,

• 		   unsigned int flags)
  

+{

• might_sleep();
• /* NOP for now. */
• return 0;

+}

2.31.1