On Fri, Aug 23, 2019 at 05:20:41PM +0100, Chris Wilson wrote:
> obj->pin_global was original used as a means to keep the shrinker off
> the active scanout, but we use the vma->pin_count itself for that and
> the obj->frontbuffer to delay shrinking active framebuffers. The other
> role that obj->pin_global gained was for spotting display objects inside
> GEM and working harder to keep those coherent; for which we can again
> simply inspect obj->frontbuffer directly.
>
> Coming up next, we will want to manipulate the pin_global counter
> outside of the principle locks, so would need to make pin_global atomic.
> However, since obj->frontbuffer is already managed atomically, it makes
> sense to use that the primary key for display objects instead of having
> pin_global.
The difference being that pin_global was only incremented while active
scanout was happening, but obj->frontbuffer simply indicates that the
obj is attached to at least one framebuffer regardless of whether it's
ever scanned out or not.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> .../gpu/drm/i915/display/intel_frontbuffer.c | 13 +++++--
> drivers/gpu/drm/i915/gem/i915_gem_domain.c | 34 ++++++-------------
> drivers/gpu/drm/i915/gem/i915_gem_object.h | 3 +-
> .../gpu/drm/i915/gem/i915_gem_object_types.h | 2 --
> drivers/gpu/drm/i915/gem/i915_gem_shrinker.c | 15 +++-----
> drivers/gpu/drm/i915/i915_debugfs.c | 12 ++-----
> 6 files changed, 29 insertions(+), 50 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_frontbuffer.c b/drivers/gpu/drm/i915/display/intel_frontbuffer.c
> index 719379774fa5..43047b676b7b 100644
> --- a/drivers/gpu/drm/i915/display/intel_frontbuffer.c
> +++ b/drivers/gpu/drm/i915/display/intel_frontbuffer.c
> @@ -220,11 +220,18 @@ static void frontbuffer_release(struct kref *ref)
> {
> struct intel_frontbuffer *front =
> container_of(ref, typeof(*front), ref);
> + struct drm_i915_gem_object *obj = front->obj;
> + struct i915_vma *vma;
>
> - front->obj->frontbuffer = NULL;
> - spin_unlock(&to_i915(front->obj->base.dev)->fb_tracking.lock);
> + spin_lock(&obj->vma.lock);
> + for_each_ggtt_vma(vma, obj)
> + vma->display_alignment = I915_GTT_PAGE_SIZE;
> + spin_unlock(&obj->vma.lock);
>
> - i915_gem_object_put(front->obj);
> + obj->frontbuffer = NULL;
> + spin_unlock(&to_i915(obj->base.dev)->fb_tracking.lock);
> +
> + i915_gem_object_put(obj);
> kfree(front);
> }
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> index 9c58e8fac1d9..0341b3da930a 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> @@ -27,7 +27,7 @@ static void __i915_gem_object_flush_for_display(struct drm_i915_gem_object *obj)
>
> void i915_gem_object_flush_if_display(struct drm_i915_gem_object *obj)
> {
> - if (!READ_ONCE(obj->pin_global))
> + if (!READ_ONCE(obj->frontbuffer))
> return;
So we maybe get a few more flushes now?
>
> i915_gem_object_lock(obj);
> @@ -422,12 +422,8 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
>
> assert_object_held(obj);
>
> - /* Mark the global pin early so that we account for the
> - * display coherency whilst setting up the cache domains.
> - */
> - obj->pin_global++;
> -
> - /* The display engine is not coherent with the LLC cache on gen6. As
> + /*
> + * The display engine is not coherent with the LLC cache on gen6. As
> * a result, we make sure that the pinning that is about to occur is
> * done with uncached PTEs. This is lowest common denominator for all
> * chipsets.
> @@ -439,12 +435,11 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
> ret = i915_gem_object_set_cache_level(obj,
> HAS_WT(to_i915(obj->base.dev)) ?
> I915_CACHE_WT : I915_CACHE_NONE);
> - if (ret) {
> - vma = ERR_PTR(ret);
> - goto err_unpin_global;
> - }
> + if (ret)
> + return ERR_PTR(ret);
>
> - /* As the user may map the buffer once pinned in the display plane
> + /*
> + * As the user may map the buffer once pinned in the display plane
> * (e.g. libkms for the bootup splash), we have to ensure that we
> * always use map_and_fenceable for all scanout buffers. However,
> * it may simply be too big to fit into mappable, in which case
> @@ -461,22 +456,19 @@ i915_gem_object_pin_to_display_plane(struct drm_i915_gem_object *obj,
> if (IS_ERR(vma))
> vma = i915_gem_object_ggtt_pin(obj, view, 0, alignment, flags);
> if (IS_ERR(vma))
> - goto err_unpin_global;
> + return vma;
>
> vma->display_alignment = max_t(u64, vma->display_alignment, alignment);
>
> __i915_gem_object_flush_for_display(obj);
>
> - /* It should now be out of any other write domains, and we can update
> + /*
> + * It should now be out of any other write domains, and we can update
> * the domain values for our changes.
> */
> obj->read_domains |= I915_GEM_DOMAIN_GTT;
>
> return vma;
> -
> -err_unpin_global:
> - obj->pin_global--;
> - return vma;
> }
>
> static void i915_gem_object_bump_inactive_ggtt(struct drm_i915_gem_object *obj)
> @@ -514,12 +506,6 @@ i915_gem_object_unpin_from_display_plane(struct i915_vma *vma)
>
> assert_object_held(obj);
>
> - if (WARN_ON(obj->pin_global == 0))
> - return;
> -
> - if (--obj->pin_global == 0)
> - vma->display_alignment = I915_GTT_MIN_ALIGNMENT;
> -
> /* Bump the LRU to try and avoid premature eviction whilst flipping */
> i915_gem_object_bump_inactive_ggtt(obj);
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> index 5efb9936e05b..d6005cad9d5c 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> @@ -406,7 +406,8 @@ static inline bool cpu_write_needs_clflush(struct drm_i915_gem_object *obj)
> if (!(obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_WRITE))
> return true;
>
> - return obj->pin_global; /* currently in use by HW, keep flushed */
> + /* Currently in use by HW (display engine)? Keep flushed. */
> + return READ_ONCE(obj->frontbuffer);
> }
>
> static inline void __start_cpu_write(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 ede0eb4218a8..13b9dc0e1a89 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> @@ -152,8 +152,6 @@ struct drm_i915_gem_object {
>
> /** Count of VMA actually bound by this object */
> atomic_t bind_count;
> - /** Count of how many global VMA are currently pinned for use by HW */
> - unsigned int pin_global;
>
> struct {
> struct mutex lock; /* protects the pages and their use */
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> index edd21d14e64f..4e55cfc2b0dc 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_shrinker.c
> @@ -61,7 +61,8 @@ static bool can_release_pages(struct drm_i915_gem_object *obj)
> if (!i915_gem_object_is_shrinkable(obj))
> return false;
>
> - /* Only report true if by unbinding the object and putting its pages
> + /*
> + * Only report true if by unbinding the object and putting its pages
> * we can actually make forward progress towards freeing physical
> * pages.
> *
> @@ -72,16 +73,8 @@ static bool can_release_pages(struct drm_i915_gem_object *obj)
> if (atomic_read(&obj->mm.pages_pin_count) > atomic_read(&obj->bind_count))
> return false;
>
> - /* If any vma are "permanently" pinned, it will prevent us from
> - * reclaiming the obj->mm.pages. We only allow scanout objects to claim
> - * a permanent pin, along with a few others like the context objects.
> - * To simplify the scan, and to avoid walking the list of vma under the
> - * object, we just check the count of its permanently pinned.
> - */
> - if (READ_ONCE(obj->pin_global))
> - return false;
Are we giving the shrinker false hope here when it comes to the actual
frontbuffer?
> -
> - /* We can only return physical pages to the system if we can either
> + /*
> + * We can only return physical pages to the system if we can either
> * discard the contents (because the user has marked them as being
> * purgeable) or if we can move their contents out to swap.
> */
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index e103fcba6435..b90371844689 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -77,11 +77,6 @@ static int i915_capabilities(struct seq_file *m, void *data)
> return 0;
> }
>
> -static char get_pin_flag(struct drm_i915_gem_object *obj)
> -{
> - return obj->pin_global ? 'p' : ' ';
> -}
> -
> static char get_tiling_flag(struct drm_i915_gem_object *obj)
> {
> switch (i915_gem_object_get_tiling(obj)) {
> @@ -140,9 +135,8 @@ describe_obj(struct seq_file *m, struct drm_i915_gem_object *obj)
> struct i915_vma *vma;
> int pin_count = 0;
>
> - seq_printf(m, "%pK: %c%c%c%c %8zdKiB %02x %02x %s%s%s",
> + seq_printf(m, "%pK: %c%c%c %8zdKiB %02x %02x %s%s%s",
> &obj->base,
> - get_pin_flag(obj),
> get_tiling_flag(obj),
> get_global_flag(obj),
> get_pin_mapped_flag(obj),
> @@ -221,8 +215,8 @@ describe_obj(struct seq_file *m, struct drm_i915_gem_object *obj)
> seq_printf(m, " (pinned x %d)", pin_count);
> if (obj->stolen)
> seq_printf(m, " (stolen: %08llx)", obj->stolen->start);
> - if (obj->pin_global)
> - seq_printf(m, " (global)");
> + if (READ_ONCE(obj->frontbuffer))
> + seq_printf(m, " (front)");
A bit confusing to say it's "front" when in fact it can be any random backbuffer.
Maybe should be just "fb" or something?
>
> engine = i915_gem_object_last_write_engine(obj);
> if (engine)
> --
> 2.23.0
>
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> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
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--
Ville Syrjälä
Intel
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