Hi Ville,
>
> 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.lankhorst@xxxxxxxxxxxxxxx>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
> > Cc: Manasi Navare <manasi.d.navare@xxxxxxxxx>
> > Signed-off-by: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
> > ---
> > 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.
[Kasireddy, Vivek] Right, bigjoiner/8K is just exposing the underlying issue; which is
that sometimes, large objects/scanout buffers that fail range overflow checks and thus
are not mappable/fenceable keep getting evicted and reinserted leading to latencies.
I guess I could mark an object/vma as permanently un-mappable/un-fenceable and try
not to map it subsequently but this would result in one scanout buffer that is mappable
but others that are not. Would this be acceptable -- assuming we are pageflipping
between multiple FBs?
Any ideas on solving this issue cleanly?
Thanks,
Vivek
>
> > +
> > 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
