| Message ID | 20220202011136.1387951-2-vivek.kasireddy@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] drm/mm: Add an iterator to optimally walk over holes for an allocation | expand |
On 02/02/2022 01:11, 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 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. > > v5: (Tvrtko) > - Rename the function to indicate that the object may be too big to > map into the aperture. > - Account for guard pages while calculating the total size required > for the object. > - Do not subject all objects to the heuristic check and instead > consider objects only of a certain size. > - Do the hole walk using the rbtree. > - Preserve the existing PIN_NONBLOCK logic. > - Drop the PIN_MAPPABLE check while pinning the VMA. Looks nice and clean. Just one question below. Sorry, it's a consequence of noticing more when it's nice and clean. :) > > 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 | 117 ++++++++++++++++++++++++-------- > 1 file changed, 88 insertions(+), 29 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index e3a2c2a0e156..752fec2b4c60 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -46,6 +46,7 @@ > #include "gem/i915_gem_mman.h" > #include "gem/i915_gem_region.h" > #include "gem/i915_gem_userptr.h" > +#include "gem/i915_gem_tiling.h" > #include "gt/intel_engine_user.h" > #include "gt/intel_gt.h" > #include "gt/intel_gt_pm.h" > @@ -876,6 +877,92 @@ static void discard_ggtt_vma(struct i915_vma *vma) > spin_unlock(&obj->vma.lock); > } > > +static bool > +i915_gem_object_fits_in_aperture(struct drm_i915_gem_object *obj, > + u64 alignment, u64 flags) > +{ > + struct drm_i915_private *i915 = to_i915(obj->base.dev); > + struct i915_ggtt *ggtt = to_gt(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; Noticed we used to report E2BIG for this case and ENOSPC for the one below. I don't know if it would be important to keep that distinction without digging into the code, but sounds plausible that it could be (for tests and such at least). To err on the side of safety it may be easier to make this helper return int 0 for success and -error? That way it's trivial to preserve the existing behaviour wrt error codes. Regards, Tvrtko > + > + /* > + * 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. > + */ > + if (!(flags & PIN_NONBLOCK)) > + return false; > + > + /* > + * We only consider objects whose size is at-least a quarter of > + * the aperture to be too big and subject them to the new > + * heuristic below. > + */ > + if (obj->base.size < ggtt->mappable_end / 4) > + return false; > + > + 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)); > + > + if (i915_vm_has_cache_coloring(&ggtt->vm)) > + fence_size += 2 * I915_GTT_PAGE_SIZE; > + > + 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_best_hole(hole, &ggtt->vm.mm, 0, ggtt->mappable_end, > + fence_size, DRM_MM_INSERT_LOW) { > + hole_start = drm_mm_hole_node_start(hole); > + hole_end = hole_start + hole->hole_size; > + > + 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, > @@ -891,36 +978,8 @@ 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_object_fits_in_aperture(obj, alignment, flags)) > 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_gem.c b/drivers/gpu/drm/i915/i915_gem.c index e3a2c2a0e156..752fec2b4c60 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -46,6 +46,7 @@ #include "gem/i915_gem_mman.h" #include "gem/i915_gem_region.h" #include "gem/i915_gem_userptr.h" +#include "gem/i915_gem_tiling.h" #include "gt/intel_engine_user.h" #include "gt/intel_gt.h" #include "gt/intel_gt_pm.h" @@ -876,6 +877,92 @@ static void discard_ggtt_vma(struct i915_vma *vma) spin_unlock(&obj->vma.lock); } +static bool +i915_gem_object_fits_in_aperture(struct drm_i915_gem_object *obj, + u64 alignment, u64 flags) +{ + struct drm_i915_private *i915 = to_i915(obj->base.dev); + struct i915_ggtt *ggtt = to_gt(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 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. + */ + if (!(flags & PIN_NONBLOCK)) + return false; + + /* + * We only consider objects whose size is at-least a quarter of + * the aperture to be too big and subject them to the new + * heuristic below. + */ + if (obj->base.size < ggtt->mappable_end / 4) + return false; + + 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)); + + if (i915_vm_has_cache_coloring(&ggtt->vm)) + fence_size += 2 * I915_GTT_PAGE_SIZE; + + 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_best_hole(hole, &ggtt->vm.mm, 0, ggtt->mappable_end, + fence_size, DRM_MM_INSERT_LOW) { + hole_start = drm_mm_hole_node_start(hole); + hole_end = hole_start + hole->hole_size; + + 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, @@ -891,36 +978,8 @@ 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_object_fits_in_aperture(obj, alignment, flags)) 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:
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. v5: (Tvrtko) - Rename the function to indicate that the object may be too big to map into the aperture. - Account for guard pages while calculating the total size required for the object. - Do not subject all objects to the heuristic check and instead consider objects only of a certain size. - Do the hole walk using the rbtree. - Preserve the existing PIN_NONBLOCK logic. - Drop the PIN_MAPPABLE check while pinning the VMA. 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 | 117 ++++++++++++++++++++++++-------- 1 file changed, 88 insertions(+), 29 deletions(-)