On Fri, 2023-06-02 at 19:50 +0300, Jani Nikula wrote:
> On Tue, 30 May 2023, Jouni Högander <jouni.hogander@xxxxxxxxx> 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?
I was thinking this as well. I couldn't figure out any other reason for
this being static inline than optimization. Maybe safest option would
still be just move it to i915_gem_object.h and have set_frontbuffer
there as well?
>
> BR,
> Jani.
>
> >
> > Signed-off-by: Jouni Högander <jouni.hogander@xxxxxxxxx>
> > ---
> > .../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);
>
