Re: [Intel-gfx] [PATCH v3 1/5] drm/i915/gem: Implement object migration

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Jun 28, 2021 at 04:46:22PM +0200, Thomas Hellström wrote:
> 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>

Looks reasonable to me as the main interface. I'm a bit on the fence on
hiding everything behind obj->ops, since we're not going to have another
implementation of migrate than the ttm one. But also while everything is
in-flight it's probably good to at least try and maintain some boundaries,
for otherwise the messiness might become unmanageable

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

But don't count this as real review :-)

One suggestion at the very bottom.

> ---
>  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;
> +	}
> +
> +	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.
> + * @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;
> +
> +	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);
> +	}
> +
> +	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. */

Maybe dma_fence_might_wait() here, since that's a notch more nasty?

Cheers, Daniel

> +	return 0;
> +}
> -- 
> 2.31.1
> 
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> Intel-gfx@lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch