| Message ID | 20211103000418.1740797-1-vivek.kasireddy@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/i915/gem: Don't try to map and fence large scanout buffers (v4) | expand |
Hi Ville, Tvrtko, Any further comments on v4 of this patch? > 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 PIN_MAPPABLE. This > results in a latency of ~10ms and happens every other vblank/repaint cycle. > Therefore, to fix this issue, we try to see if there is space to map > at-least two objects of a given size and return early if there isn't. This > would ensure that we do not try with PIN_MAPPABLE for any objects that > are too big to map thereby preventing unncessary unbind. > > 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 are 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 | } > > v2: Instead of using bigjoiner checks, determine whether a scanout > buffer is too big by checking to see if it is possible to map > two of them into the ggtt. > > v3 (Ville): > - Count how many fb objects can be fit into the available holes > instead of checking for a hole twice the object size. > - Take alignment constraints into account. > - Limit this large scanout buffer check to >= Gen 11 platforms. > > v4: > - Remove existing heuristic that checks just for size. (Ville) > - Return early if we find space to map at-least two objects. (Tvrtko) > - Slightly update the commit message. > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> > Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> > Cc: Manasi Navare <manasi.d.navare@intel.com> > Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com> > --- > drivers/gpu/drm/i915/i915_gem.c | 87 ++++++++++++++++++++++----------- > drivers/gpu/drm/i915/i915_vma.c | 2 +- > 2 files changed, 59 insertions(+), 30 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index d0e642c82064..287508c37a9a 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -866,6 +866,63 @@ static void discard_ggtt_vma(struct i915_vma *vma) > spin_unlock(&obj->vma.lock); > } > > +static bool i915_gem_obj_too_big(struct drm_i915_gem_object *obj, > + u64 alignment) > +{ > + struct drm_i915_private *i915 = to_i915(obj->base.dev); > + struct i915_ggtt *ggtt = &i915->ggtt; > + struct drm_mm_node *hole; > + u64 hole_start, hole_end, start, end; > + u64 fence_size, fence_alignment; > + unsigned int count = 0; > + > + /* > + * If the required space is larger than the available > + * aperture, we will not able to find a slot for the > + * object and unbinding the object now will be in > + * vain. Worse, doing so may cause us to ping-pong > + * the object in and out of the Global GTT and > + * waste a lot of cycles under the mutex. > + */ > + if (obj->base.size > ggtt->mappable_end) > + return true; > + > + if (HAS_GMCH(i915) || DISPLAY_VER(i915) < 11 || > + !i915_gem_object_is_framebuffer(obj)) > + return false; > + > + fence_size = i915_gem_fence_size(i915, obj->base.size, > + i915_gem_object_get_tiling(obj), > + i915_gem_object_get_stride(obj)); > + fence_alignment = i915_gem_fence_alignment(i915, obj->base.size, > + i915_gem_object_get_tiling(obj), > + i915_gem_object_get_stride(obj)); > + alignment = max_t(u64, alignment, fence_alignment); > + > + /* > + * Assuming this object is a large scanout buffer, we try to find > + * out if there is room to map at-least two of them. There could > + * be space available to map one but to be consistent, we try to > + * avoid mapping/fencing any of them. > + */ > + drm_mm_for_each_hole(hole, &ggtt->vm.mm, hole_start, hole_end) { > + do { > + start = round_up(hole_start, alignment); > + end = min_t(u64, hole_end, ggtt->mappable_end); > + > + if (range_overflows(start, fence_size, end)) > + break; > + > + if (++count >= 2) > + return false; > + > + hole_start = start + fence_size; > + } while (1); > + } > + > + return true; > +} > + > struct i915_vma * > i915_gem_object_ggtt_pin_ww(struct drm_i915_gem_object *obj, > struct i915_gem_ww_ctx *ww, > @@ -879,36 +936,8 @@ i915_gem_object_ggtt_pin_ww(struct drm_i915_gem_object > *obj, > > if (flags & PIN_MAPPABLE && > (!view || view->type == I915_GGTT_VIEW_NORMAL)) { > - /* > - * If the required space is larger than the available > - * aperture, we will not able to find a slot for the > - * object and unbinding the object now will be in > - * vain. Worse, doing so may cause us to ping-pong > - * the object in and out of the Global GTT and > - * waste a lot of cycles under the mutex. > - */ > - if (obj->base.size > ggtt->mappable_end) > + if (i915_gem_obj_too_big(obj, alignment)) > return ERR_PTR(-E2BIG); > - > - /* > - * If NONBLOCK is set the caller is optimistically > - * trying to cache the full object within the mappable > - * aperture, and *must* have a fallback in place for > - * situations where we cannot bind the object. We > - * can be a little more lax here and use the fallback > - * more often to avoid costly migrations of ourselves > - * and other objects within the aperture. > - * > - * Half-the-aperture is used as a simple heuristic. > - * More interesting would to do search for a free > - * block prior to making the commitment to unbind. > - * That caters for the self-harm case, and with a > - * little more heuristics (e.g. NOFAULT, NOEVICT) > - * we could try to minimise harm to others. > - */ > - if (flags & PIN_NONBLOCK && > - obj->base.size > ggtt->mappable_end / 2) > - return ERR_PTR(-ENOSPC); > } > > new_vma: > diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c > index 90546fa58fc1..551644dbfa8a 100644 > --- a/drivers/gpu/drm/i915/i915_vma.c > +++ b/drivers/gpu/drm/i915/i915_vma.c > @@ -977,7 +977,7 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct > i915_gem_ww_ctx *ww, > if (err) > goto err_active; > > - if (i915_is_ggtt(vma->vm)) > + if (i915_is_ggtt(vma->vm) && flags & PIN_MAPPABLE) > __i915_vma_set_map_and_fenceable(vma); > } > > -- > 2.31.1
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index d0e642c82064..287508c37a9a 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -866,6 +866,63 @@ static void discard_ggtt_vma(struct i915_vma *vma) spin_unlock(&obj->vma.lock); } +static bool i915_gem_obj_too_big(struct drm_i915_gem_object *obj, + u64 alignment) +{ + struct drm_i915_private *i915 = to_i915(obj->base.dev); + struct i915_ggtt *ggtt = &i915->ggtt; + struct drm_mm_node *hole; + u64 hole_start, hole_end, start, end; + u64 fence_size, fence_alignment; + unsigned int count = 0; + + /* + * If the required space is larger than the available + * aperture, we will not able to find a slot for the + * object and unbinding the object now will be in + * vain. Worse, doing so may cause us to ping-pong + * the object in and out of the Global GTT and + * waste a lot of cycles under the mutex. + */ + if (obj->base.size > ggtt->mappable_end) + return true; + + if (HAS_GMCH(i915) || DISPLAY_VER(i915) < 11 || + !i915_gem_object_is_framebuffer(obj)) + return false; + + fence_size = i915_gem_fence_size(i915, obj->base.size, + i915_gem_object_get_tiling(obj), + i915_gem_object_get_stride(obj)); + fence_alignment = i915_gem_fence_alignment(i915, obj->base.size, + i915_gem_object_get_tiling(obj), + i915_gem_object_get_stride(obj)); + alignment = max_t(u64, alignment, fence_alignment); + + /* + * Assuming this object is a large scanout buffer, we try to find + * out if there is room to map at-least two of them. There could + * be space available to map one but to be consistent, we try to + * avoid mapping/fencing any of them. + */ + drm_mm_for_each_hole(hole, &ggtt->vm.mm, hole_start, hole_end) { + do { + start = round_up(hole_start, alignment); + end = min_t(u64, hole_end, ggtt->mappable_end); + + if (range_overflows(start, fence_size, end)) + break; + + if (++count >= 2) + return false; + + hole_start = start + fence_size; + } while (1); + } + + return true; +} + struct i915_vma * i915_gem_object_ggtt_pin_ww(struct drm_i915_gem_object *obj, struct i915_gem_ww_ctx *ww, @@ -879,36 +936,8 @@ i915_gem_object_ggtt_pin_ww(struct drm_i915_gem_object *obj, if (flags & PIN_MAPPABLE && (!view || view->type == I915_GGTT_VIEW_NORMAL)) { - /* - * If the required space is larger than the available - * aperture, we will not able to find a slot for the - * object and unbinding the object now will be in - * vain. Worse, doing so may cause us to ping-pong - * the object in and out of the Global GTT and - * waste a lot of cycles under the mutex. - */ - if (obj->base.size > ggtt->mappable_end) + if (i915_gem_obj_too_big(obj, alignment)) return ERR_PTR(-E2BIG); - - /* - * If NONBLOCK is set the caller is optimistically - * trying to cache the full object within the mappable - * aperture, and *must* have a fallback in place for - * situations where we cannot bind the object. We - * can be a little more lax here and use the fallback - * more often to avoid costly migrations of ourselves - * and other objects within the aperture. - * - * Half-the-aperture is used as a simple heuristic. - * More interesting would to do search for a free - * block prior to making the commitment to unbind. - * That caters for the self-harm case, and with a - * little more heuristics (e.g. NOFAULT, NOEVICT) - * we could try to minimise harm to others. - */ - if (flags & PIN_NONBLOCK && - obj->base.size > ggtt->mappable_end / 2) - return ERR_PTR(-ENOSPC); } new_vma: diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c index 90546fa58fc1..551644dbfa8a 100644 --- a/drivers/gpu/drm/i915/i915_vma.c +++ b/drivers/gpu/drm/i915/i915_vma.c @@ -977,7 +977,7 @@ int i915_vma_pin_ww(struct i915_vma *vma, struct i915_gem_ww_ctx *ww, if (err) goto err_active; - if (i915_is_ggtt(vma->vm)) + if (i915_is_ggtt(vma->vm) && flags & PIN_MAPPABLE) __i915_vma_set_map_and_fenceable(vma); }
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 PIN_MAPPABLE. This results in a latency of ~10ms and happens every other vblank/repaint cycle. Therefore, to fix this issue, we try to see if there is space to map at-least two objects of a given size and return early if there isn't. This would ensure that we do not try with PIN_MAPPABLE for any objects that are too big to map thereby preventing unncessary unbind. 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 are 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 | } v2: Instead of using bigjoiner checks, determine whether a scanout buffer is too big by checking to see if it is possible to map two of them into the ggtt. v3 (Ville): - Count how many fb objects can be fit into the available holes instead of checking for a hole twice the object size. - Take alignment constraints into account. - Limit this large scanout buffer check to >= Gen 11 platforms. v4: - Remove existing heuristic that checks just for size. (Ville) - Return early if we find space to map at-least two objects. (Tvrtko) - Slightly update the commit message. Cc: Ville Syrjälä <ville.syrjala@linux.intel.com> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> Cc: Manasi Navare <manasi.d.navare@intel.com> Signed-off-by: Vivek Kasireddy <vivek.kasireddy@intel.com> --- drivers/gpu/drm/i915/i915_gem.c | 87 ++++++++++++++++++++++----------- drivers/gpu/drm/i915/i915_vma.c | 2 +- 2 files changed, 59 insertions(+), 30 deletions(-)