On Tue, 30 May 2023, Jouni Högander <jouni.hogan...@intel.com> wrote:
> Add getter/setter for i915_gem_object->frontbuffer and use it instead of
> directly touching i915_gem_object->frontbuffer frontbuffer pointer.
Before going into the details (which, at a glance, look fine) I think we
need to talk about the potential performance impact. I've never seen any
other reason for the static inlines here than avoiding a function call
when possible. Are there any other reasons? Is that a useless
micro-optimization or something that could have an impact? On what?
BR,
Jani.
>
> Signed-off-by: Jouni Högander <jouni.hogan...@intel.com>
> ---
> .../gpu/drm/i915/display/intel_frontbuffer.c | 18 ++---
> .../gpu/drm/i915/display/intel_frontbuffer.h | 27 -------
> drivers/gpu/drm/i915/gem/i915_gem_object.c | 70 ++++++++++++++++++-
> drivers/gpu/drm/i915/gem/i915_gem_object.h | 6 ++
> drivers/gpu/drm/i915/i915_vma.c | 2 +-
> 5 files changed, 81 insertions(+), 42 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_frontbuffer.c
> b/drivers/gpu/drm/i915/display/intel_frontbuffer.c
> index 3ce0436a0c7d..41ac65c98720 100644
> --- a/drivers/gpu/drm/i915/display/intel_frontbuffer.c
> +++ b/drivers/gpu/drm/i915/display/intel_frontbuffer.c
> @@ -237,7 +237,7 @@ static void frontbuffer_release(struct kref *ref)
> }
> spin_unlock(&obj->vma.lock);
>
> - RCU_INIT_POINTER(obj->frontbuffer, NULL);
> + i915_gem_object_set_frontbuffer(obj, NULL);
> spin_unlock(&intel_bo_to_i915(obj)->display.fb_tracking.lock);
>
> i915_active_fini(&front->write);
> @@ -250,9 +250,9 @@ struct intel_frontbuffer *
> intel_frontbuffer_get(struct drm_i915_gem_object *obj)
> {
> struct drm_i915_private *i915 = intel_bo_to_i915(obj);
> - struct intel_frontbuffer *front;
> + struct intel_frontbuffer *front, *front_ret;
>
> - front = __intel_frontbuffer_get(obj);
> + front = i915_gem_object_get_frontbuffer(obj);
> if (front)
> return front;
>
> @@ -269,16 +269,10 @@ intel_frontbuffer_get(struct drm_i915_gem_object *obj)
> I915_ACTIVE_RETIRE_SLEEPS);
>
> spin_lock(&i915->display.fb_tracking.lock);
> - if (rcu_access_pointer(obj->frontbuffer)) {
> - kfree(front);
> - front = rcu_dereference_protected(obj->frontbuffer, true);
> - kref_get(&front->ref);
> - } else {
> - i915_gem_object_get(obj);
> - rcu_assign_pointer(obj->frontbuffer, front);
> - }
> + front_ret = i915_gem_object_set_frontbuffer(obj, front);
> spin_unlock(&i915->display.fb_tracking.lock);
> -
> + if (front_ret != front)
> + kfree(front);
> return front;
> }
>
> diff --git a/drivers/gpu/drm/i915/display/intel_frontbuffer.h
> b/drivers/gpu/drm/i915/display/intel_frontbuffer.h
> index 3c474ed937fb..eeccc847331d 100644
> --- a/drivers/gpu/drm/i915/display/intel_frontbuffer.h
> +++ b/drivers/gpu/drm/i915/display/intel_frontbuffer.h
> @@ -75,33 +75,6 @@ void intel_frontbuffer_flip(struct drm_i915_private *i915,
>
> void intel_frontbuffer_put(struct intel_frontbuffer *front);
>
> -static inline struct intel_frontbuffer *
> -__intel_frontbuffer_get(const struct drm_i915_gem_object *obj)
> -{
> - struct intel_frontbuffer *front;
> -
> - if (likely(!rcu_access_pointer(obj->frontbuffer)))
> - return NULL;
> -
> - rcu_read_lock();
> - do {
> - front = rcu_dereference(obj->frontbuffer);
> - if (!front)
> - break;
> -
> - if (unlikely(!kref_get_unless_zero(&front->ref)))
> - continue;
> -
> - if (likely(front == rcu_access_pointer(obj->frontbuffer)))
> - break;
> -
> - intel_frontbuffer_put(front);
> - } while (1);
> - rcu_read_unlock();
> -
> - return front;
> -}
> -
> struct intel_frontbuffer *
> intel_frontbuffer_get(struct drm_i915_gem_object *obj);
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> index 46a19b099ec8..6945e903e106 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
> @@ -463,7 +463,7 @@ void __i915_gem_object_flush_frontbuffer(struct
> drm_i915_gem_object *obj,
> {
> struct intel_frontbuffer *front;
>
> - front = __intel_frontbuffer_get(obj);
> + front = i915_gem_object_get_frontbuffer(obj);
> if (front) {
> intel_frontbuffer_flush(front, origin);
> intel_frontbuffer_put(front);
> @@ -475,7 +475,7 @@ void __i915_gem_object_invalidate_frontbuffer(struct
> drm_i915_gem_object *obj,
> {
> struct intel_frontbuffer *front;
>
> - front = __intel_frontbuffer_get(obj);
> + front = i915_gem_object_get_frontbuffer(obj);
> if (front) {
> intel_frontbuffer_invalidate(front, origin);
> intel_frontbuffer_put(front);
> @@ -952,6 +952,72 @@ bool i915_gem_object_has_unknown_state(struct
> drm_i915_gem_object *obj)
> return obj->mm.unknown_state;
> }
>
> +/**
> + * i915_gem_object_get_frontbuffer - Get the object's frontbuffer
> + * @obj: The object whose frontbuffer to get.
> + *
> + * Get pointer to object's frontbuffer if such exists. Please note that RCU
> + * mechanism is used to handle e.g. ongoing removal of frontbuffer pointer.
> + *
> + * Return: pointer to object's frontbuffer is such exists or NULL
> + */
> +struct intel_frontbuffer *
> +i915_gem_object_get_frontbuffer(const struct drm_i915_gem_object *obj)
> +{
> + struct intel_frontbuffer *front;
> +
> + if (likely(!rcu_access_pointer(obj->frontbuffer)))
> + return NULL;
> +
> + rcu_read_lock();
> + do {
> + front = rcu_dereference(obj->frontbuffer);
> + if (!front)
> + break;
> +
> + if (unlikely(!kref_get_unless_zero(&front->ref)))
> + continue;
> +
> + if (likely(front == rcu_access_pointer(obj->frontbuffer)))
> + break;
> +
> + intel_frontbuffer_put(front);
> + } while (1);
> + rcu_read_unlock();
> +
> + return front;
> +}
> +
> +/**
> + * i915_gem_object_set_frontbuffer - Set the object's frontbuffer
> + * @obj: The object whose frontbuffer to set.
> + * @front: The frontbuffer to set
> + *
> + * Set object's frontbuffer pointer. If frontbuffer is already set for the
> + * object keep it and return it's pointer to the caller. Please note that RCU
> + * mechanism is used to handle e.g. ongoing removal of frontbuffer pointer.
> + *
> + * Return: pointer to frontbuffer which was set.
> + */
> +struct intel_frontbuffer *
> +i915_gem_object_set_frontbuffer(struct drm_i915_gem_object *obj,
> + struct intel_frontbuffer *front)
> +{
> + struct intel_frontbuffer *front_ret = front;
> +
> + if (!front) {
> + RCU_INIT_POINTER(obj->frontbuffer, NULL);
> + } else if (rcu_access_pointer(obj->frontbuffer)) {
> + front_ret = rcu_dereference_protected(obj->frontbuffer, true);
> + kref_get(&front_ret->ref);
> + } else {
> + drm_gem_object_get(&intel_bo_to_drm_bo(obj));
> + rcu_assign_pointer(obj->frontbuffer, front);
> + }
> +
> + return front_ret;
> +}
> +
> #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
> #include "selftests/huge_gem_object.c"
> #include "selftests/huge_pages.c"
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> index 884a17275b3a..69c5fa91152a 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> @@ -891,4 +891,10 @@ static inline int
> i915_gem_object_userptr_validate(struct drm_i915_gem_object *o
>
> #endif
>
> +struct intel_frontbuffer *
> +i915_gem_object_get_frontbuffer(const struct drm_i915_gem_object *obj);
> +struct intel_frontbuffer *
> +i915_gem_object_set_frontbuffer(struct drm_i915_gem_object *obj,
> + struct intel_frontbuffer *front);
> +
> #endif
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index ffb425ba591c..c66ff2157f6a 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -1908,7 +1908,7 @@ int _i915_vma_move_to_active(struct i915_vma *vma,
> if (flags & EXEC_OBJECT_WRITE) {
> struct intel_frontbuffer *front;
>
> - front = __intel_frontbuffer_get(obj);
> + front = i915_gem_object_get_frontbuffer(obj);
> if (unlikely(front)) {
> if (intel_frontbuffer_invalidate(front, ORIGIN_CS))
> i915_active_add_request(&front->write, rq);
--
Jani Nikula, Intel Open Source Graphics Center
