On Mon, Oct 25, 2021 at 11:38:11PM -0700, Vivek Kasireddy wrote:
> On platforms capable of allowing 8K (7680 x 4320) modes, pinning 2 or
> more framebuffers/scanout buffers results in only one that is mappable/
> fenceable. Therefore, pageflipping between these 2 FBs where only one
> is mappable/fenceable creates latencies large enough to miss alternate
> vblanks thereby producing less optimal framerate.
>
> This mainly happens because when i915_gem_object_pin_to_display_plane()
> is called to pin one of the FB objs, the associated vma is identified
> as misplaced and therefore i915_vma_unbind() is called which unbinds and
> evicts it. This misplaced vma gets subseqently pinned only when
> i915_gem_object_ggtt_pin_ww() is called without the mappable flag. This
> results in a latency of ~10ms and happens every other vblank/repaint cycle.
>
> Testcase:
> Running Weston and weston-simple-egl on an Alderlake_S (ADLS) platform
> with a 8K@60 mode results in only ~40 FPS. Since upstream Weston submits
> a frame ~7ms before the next vblank, the latencies seen between atomic
> commit and flip event is 7, 24 (7 + 16.66), 7, 24..... suggesting that
> it misses the vblank every other frame.
>
> Here is the ftrace snippet that shows the source of the ~10ms latency:
> i915_gem_object_pin_to_display_plane() {
> 0.102 us | i915_gem_object_set_cache_level();
> i915_gem_object_ggtt_pin_ww() {
> 0.390 us | i915_vma_instance();
> 0.178 us | i915_vma_misplaced();
> i915_vma_unbind() {
> __i915_active_wait() {
> 0.082 us | i915_active_acquire_if_busy();
> 0.475 us | }
> intel_runtime_pm_get() {
> 0.087 us | intel_runtime_pm_acquire();
> 0.259 us | }
> __i915_active_wait() {
> 0.085 us | i915_active_acquire_if_busy();
> 0.240 us | }
> __i915_vma_evict() {
> ggtt_unbind_vma() {
> gen8_ggtt_clear_range() {
> 10507.255 us | }
> 10507.689 us | }
> 10508.516 us | }
>
> Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursu...@linux.intel.com>
> Cc: Manasi Navare <manasi.d.nav...@intel.com>
> Signed-off-by: Vivek Kasireddy <vivek.kasire...@intel.com>
> ---
> drivers/gpu/drm/i915/display/intel_fb_pin.c | 11 +++++++++--
> drivers/gpu/drm/i915/display/intel_overlay.c | 11 ++++++++---
> drivers/gpu/drm/i915/gem/i915_gem_domain.c | 6 ++++--
> drivers/gpu/drm/i915/gem/i915_gem_object.h | 3 ++-
> 4 files changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_fb_pin.c
> b/drivers/gpu/drm/i915/display/intel_fb_pin.c
> index 3f77f3013584..53c156d9a9f9 100644
> --- a/drivers/gpu/drm/i915/display/intel_fb_pin.c
> +++ b/drivers/gpu/drm/i915/display/intel_fb_pin.c
> @@ -144,7 +144,7 @@ intel_pin_and_fence_fb_obj(struct drm_framebuffer *fb,
>
> if (!ret) {
> vma = i915_gem_object_pin_to_display_plane(obj, &ww, alignment,
> - view, pinctl);
> + view, pinctl,
> uses_fence);
> if (IS_ERR(vma)) {
> ret = PTR_ERR(vma);
> goto err_unpin;
> @@ -218,9 +218,16 @@ int intel_plane_pin_fb(struct intel_plane_state
> *plane_state)
> INTEL_INFO(dev_priv)->display.cursor_needs_physical;
>
> if (!intel_fb_uses_dpt(fb)) {
> + struct intel_crtc *crtc = to_intel_crtc(plane_state->hw.crtc);
> + struct intel_crtc_state *crtc_state =
> + to_intel_crtc_state(crtc->base.state);
> + bool uses_fence = intel_plane_uses_fence(plane_state);
> + bool is_bigjoiner = crtc_state->bigjoiner ||
> + crtc_state->bigjoiner_slave;
Bigjoiner is just an implementation detail. It is not the cause of any
of this.
> +
> vma = intel_pin_and_fence_fb_obj(fb, phys_cursor,
> &plane_state->view.gtt,
> -
> intel_plane_uses_fence(plane_state),
> + uses_fence && !is_bigjoiner,
> &plane_state->flags);
> if (IS_ERR(vma))
> return PTR_ERR(vma);
> diff --git a/drivers/gpu/drm/i915/display/intel_overlay.c
> b/drivers/gpu/drm/i915/display/intel_overlay.c
> index 7e3f5c6ca484..e9563b40b911 100644
> --- a/drivers/gpu/drm/i915/display/intel_overlay.c
> +++ b/drivers/gpu/drm/i915/display/intel_overlay.c
> @@ -755,10 +755,14 @@ static u32 overlay_cmd_reg(struct
> drm_intel_overlay_put_image *params)
> return cmd;
> }
>
> -static struct i915_vma *intel_overlay_pin_fb(struct drm_i915_gem_object
> *new_bo)
> +static struct i915_vma *intel_overlay_pin_fb(struct drm_i915_gem_object
> *new_bo,
> + struct intel_overlay *overlay)
> {
> struct i915_gem_ww_ctx ww;
> struct i915_vma *vma;
> + const struct intel_plane_state *plane_state =
> + to_intel_plane_state(overlay->crtc->base.primary->state);
> + bool uses_fence = intel_plane_uses_fence(plane_state);
> int ret;
>
> i915_gem_ww_ctx_init(&ww, true);
> @@ -766,7 +770,8 @@ static struct i915_vma *intel_overlay_pin_fb(struct
> drm_i915_gem_object *new_bo)
> ret = i915_gem_object_lock(new_bo, &ww);
> if (!ret) {
> vma = i915_gem_object_pin_to_display_plane(new_bo, &ww, 0,
> - NULL, PIN_MAPPABLE);
> + NULL, PIN_MAPPABLE,
> + uses_fence);
> ret = PTR_ERR_OR_ZERO(vma);
> }
> if (ret == -EDEADLK) {
> @@ -802,7 +807,7 @@ static int intel_overlay_do_put_image(struct
> intel_overlay *overlay,
>
> atomic_inc(&dev_priv->gpu_error.pending_fb_pin);
>
> - vma = intel_overlay_pin_fb(new_bo);
> + vma = intel_overlay_pin_fb(new_bo, overlay);
> if (IS_ERR(vma)) {
> ret = PTR_ERR(vma);
> goto out_pin_section;
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> index b684a62bf3b0..b9108f13cc49 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_domain.c
> @@ -375,7 +375,8 @@ i915_gem_object_pin_to_display_plane(struct
> drm_i915_gem_object *obj,
> struct i915_gem_ww_ctx *ww,
> u32 alignment,
> const struct i915_ggtt_view *view,
> - unsigned int flags)
> + unsigned int flags,
> + bool uses_fence)
> {
> struct drm_i915_private *i915 = to_i915(obj->base.dev);
> struct i915_vma *vma;
> @@ -411,7 +412,8 @@ i915_gem_object_pin_to_display_plane(struct
> drm_i915_gem_object *obj,
> */
> vma = ERR_PTR(-ENOSPC);
> if ((flags & PIN_MAPPABLE) == 0 &&
> - (!view || view->type == I915_GGTT_VIEW_NORMAL))
> + (!view || view->type == I915_GGTT_VIEW_NORMAL) &&
> + uses_fence)
> vma = i915_gem_object_ggtt_pin_ww(obj, ww, view, 0, alignment,
> flags | PIN_MAPPABLE |
> PIN_NONBLOCK);
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> index a5479ac7a4ad..e83564fa57ca 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> @@ -534,7 +534,8 @@ i915_gem_object_pin_to_display_plane(struct
> drm_i915_gem_object *obj,
> struct i915_gem_ww_ctx *ww,
> u32 alignment,
> const struct i915_ggtt_view *view,
> - unsigned int flags);
> + unsigned int flags,
> + bool uses_fence);
>
> void i915_gem_object_make_unshrinkable(struct drm_i915_gem_object *obj);
> void i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj);
> --
> 2.31.1
--
Ville Syrjälä
Intel
