On 07/02/2022 10:58, Ville Syrjälä wrote:
On Thu, Feb 03, 2022 at 05:22:10PM -0800, 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. v6: (Tvrtko) - Return 0 on success and the specific error code on failure to preserve the existing behavior. Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> 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/i915_gem.c | 120 ++++++++++++++++++++++++-------- 1 file changed, 90 insertions(+), 30 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index e3a2c2a0e156..39f0d17550c3 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 int+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 -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. + */ + if (!(flags & PIN_NONBLOCK)) + return 0; + + /* + * 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 0;That seems a fairly arbitrary thing to put here. Maybe something the caller should check/specify?
I have no strong opinion on this one. In my mind I categorised it under "is it a large framebuffer" heuristics. Previously it was less than one half of aperture always okay, now one quarter, plus 2x hole check if larger. Both are heuristics. I even mentioned earlier if 2x should be an input parameter as well, but again, given it's not an exported function couldn't really justify it.
+ + if (HAS_GMCH(i915) || DISPLAY_VER(i915) < 11 || + !i915_gem_object_is_framebuffer(obj)) + return 0;None of that seems appropriate for a generic gem function with this name.
It's not exported though, maybe remove i915_gem prefix to avoid any ideas of it being generic?
Regards, Tvrtko
+ + 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_suitable_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 0; + + hole_start = start + fence_size; + } while (1); + } + + return -ENOSPC; +} + struct i915_vma * i915_gem_object_ggtt_pin_ww(struct drm_i915_gem_object *obj, struct i915_gem_ww_ctx *ww, @@ -891,36 +978,9 @@ 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) - 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); + ret = i915_gem_object_fits_in_aperture(obj, alignment, flags); + if (ret) + return ERR_PTR(ret); }new_vma:-- 2.34.1
