On ke, 2016-09-14 at 07:52 +0100, Chris Wilson wrote:
> In preparation to support many distinct timelines, we need to expand the
> activity tracking on the GEM object to handle more than just a request
> per engine. We already use the struct reservation_object on the dma-buf
> to handle many fence contexts, so integrating that into the GEM object
> itself is the preferred solution. (For example, we can now share the same
> reservation_object between every consumer/producer using this buffer and
> skip the manual import/export via dma-buf.)
>
> Caveats:
I'd make comments which patch in the series addresses each introduced
problem, which are fixable in future and which are taken as "a
permanent hit" for achieving multiple timelines. With a bit of
reasoning for each (now only a few points include some of this).
> static inline struct drm_i915_gem_object *
> @@ -2347,35 +2341,10 @@ i915_gem_object_has_struct_page(const struct drm_i915_gem_object *obj)
> return obj->ops->flags & I915_GEM_OBJECT_HAS_STRUCT_PAGE;
> }
>
> -static inline unsigned long
> -i915_gem_object_get_active(const struct drm_i915_gem_object *obj)
> -{
> - return (obj->flags >> I915_BO_ACTIVE_SHIFT) & I915_BO_ACTIVE_MASK;
> -}
> -
> static inline bool
> i915_gem_object_is_active(const struct drm_i915_gem_object *obj)
> {
> - return i915_gem_object_get_active(obj);
> -}
> -
> -static inline void
> -i915_gem_object_set_active(struct drm_i915_gem_object *obj, int engine)
> -{
> - obj->flags |= BIT(engine + I915_BO_ACTIVE_SHIFT);
> -}
> -
> -static inline void
> -i915_gem_object_clear_active(struct drm_i915_gem_object *obj, int engine)
> -{
> - obj->flags &= ~BIT(engine + I915_BO_ACTIVE_SHIFT);
> -}
> -
> -static inline bool
> -i915_gem_object_has_active_engine(const struct drm_i915_gem_object *obj,
> - int engine)
> -{
> - return obj->flags & BIT(engine + I915_BO_ACTIVE_SHIFT);
> + return obj->active_count;
our type is bool, so !!obj->active_count;
> }
>
<SNIP>
>
> static int
> i915_gem_execbuffer_move_to_gpu(struct drm_i915_gem_request *req,
> struct list_head *vmas)
> {
> - const unsigned int other_rings = eb_other_engines(req);
> struct i915_vma *vma;
> int ret;
>
> list_for_each_entry(vma, vmas, exec_list) {
> struct drm_i915_gem_object *obj = vma->obj;
> - struct reservation_object *resv;
> -
> - if (obj->flags & other_rings) {
> - ret = i915_gem_request_await_object
> - (req, obj, obj->base.pending_write_domain);
> - if (ret)
> - return ret;
> - }
>
> - resv = i915_gem_object_get_dmabuf_resv(obj);
> - if (resv) {
> - ret = i915_sw_fence_await_reservation
> - (&req->submit, resv, &i915_fence_ops,
> - obj->base.pending_write_domain, 10*HZ,
> - GFP_KERNEL | __GFP_NOWARN);
> - if (ret < 0)
> - return ret;
> - }
> + ret = i915_gem_request_await_object
> + (req, obj, obj->base.pending_write_domain);
I know it was previously like this, but I'm not sure I agree on this
style at all.
> @@ -11935,17 +11932,8 @@ static bool use_mmio_flip(struct intel_engine_cs *engine,
>
> if (i915.use_mmio_flip < 0)
> return false;
> - else if (i915.use_mmio_flip > 0)
> - return true;
> - else if (i915.enable_execlists)
> - return true;
>
> - resv = i915_gem_object_get_dmabuf_resv(obj);
> - if (resv && !reservation_object_test_signaled_rcu(resv, false))
> - return true;
> -
> - return engine != i915_gem_active_get_engine(&obj->last_write,
> - &obj->base.dev->struct_mutex);
> + return true;
return i915_use_mmio_flip >= 0; // ?
> @@ -860,39 +860,6 @@ struct drm_i915_gem_busy {
> * long as no new GPU commands are executed upon it). Due to the
> * asynchronous nature of the hardware, an object reported
> * as busy may become idle before the ioctl is completed.
> - *
> - * Furthermore, if the object is busy, which engine is busy is only
> - * provided as a guide. There are race conditions which prevent the
> - * report of which engines are busy from being always accurate.
> - * However, the converse is not true. If the object is idle, the
> - * result of the ioctl, that all engines are idle, is accurate.
> - *
> - * The returned dword is split into two fields to indicate both
> - * the engines on which the object is being read, and the
> - * engine on which it is currently being written (if any).
> - *
> - * The low word (bits 0:15) indicate if the object is being written
> - * to by any engine (there can only be one, as the GEM implicit
> - * synchronisation rules force writes to be serialised). Only the
> - * engine for the last write is reported.
> - *
> - * The high word (bits 16:31) are a bitmask of which engines are
> - * currently reading from the object. Multiple engines may be
> - * reading from the object simultaneously.
> - *
> - * The value of each engine is the same as specified in the
> - * EXECBUFFER2 ioctl, i.e. I915_EXEC_RENDER, I915_EXEC_BSD etc.
> - * Note I915_EXEC_DEFAULT is a symbolic value and is mapped to
> - * the I915_EXEC_RENDER engine for execution, and so it is never
> - * reported as active itself. Some hardware may have parallel
> - * execution engines, e.g. multiple media engines, which are
> - * mapped to the same identifier in the EXECBUFFER2 ioctl and
> - * so are not separately reported for busyness.
> - *
> - * Caveat emptor:
> - * Only the boolean result of this query is reliable; that is whether
> - * the object is idle or busy. The report of which engines are busy
> - * should be only used as a heuristic.
> */
Daniel to Ack this ABI change.
Reviewed-by: Joonas Lahtinen <joonas.lahtine@xxxxxxxxxxxxxxx>
Double check by somebody on the plane code would not hurt.
Regards, Joonas
--
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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