On Thu, Feb 16, 2023 at 10:59:12AM +0000, Tvrtko Ursulin wrote: > From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > > In i915 we have this concept of "wait boosting" where we give a priority boost > for instance to fences which are actively waited upon from userspace. This has > it's pros and cons and can certainly be discussed at lenght. However fact is > some workloads really like it. > > Problem is that with the arrival of drm syncobj and a new userspace waiting > entry point it added, the waitboost mechanism was bypassed. AFAIU this mostly > happens with all Vulkan based userspaces. Hence I cooked up this mini series to > see if discussion about restoring the waitboost can be had. > > The series adds a concept of "wait count" to dma fence which is intended to > represent explicit userspace waits. It is therefore incremented for every > explicit dma_fence_enable_sw_signaling and dma_fence_add_wait_callback (like > dma_fence_add_callback but from explicit/userspace wait paths). Individual > drivers can then inspect this via dma_fence_wait_count() and decide to wait > boost the waits on such fences. > > Patch has been slightly tested for performance impact by Google using some clvk > workloads and shows a good improvement (frame time improved from 16ms to 13ms). > > It is also important to mention that benefits of waitboosting are not only about > workloads related to frame presentation time, but also for serialized > computations which constantly move between the CPU and GPU. I think this should be integrated with https://lore.kernel.org/all/20210903184806.1680887-1-robdclark@xxxxxxxxx/ so that we have one overall approach here that works for all drivers. Obviously should include support for all interested parties. -Daniel > > *) > https://gitlab.freedesktop.org/drm/intel/-/issues/8014 > > v2: > * Small fixups based on CI feedback: > * Handle decrement correctly for already signalled case while adding callback. > * Remove i915 assert which was making sure struct i915_request does not grow. > * Split out the i915 patch into three separate functional changes. > > v3: > * Handle drivers which open-code callback additions. > > Tvrtko Ursulin (9): > dma-fence: Move i915 helpers into common > dma-fence: Add callback initialization helper > drm/i915: Use fence callback initialization helper > drm/vmwgfx: Use fence callback initialization helper > dma-fence: Track explicit waiters > drm/syncobj: Mark syncobj waits as external waiters > drm/i915: Waitboost external waits > drm/i915: Mark waits as explicit > drm/i915: Wait boost requests waited upon by others > > drivers/dma-buf/dma-fence.c | 137 ++++++++++++++------ > drivers/gpu/drm/drm_syncobj.c | 6 +- > drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 22 ---- > drivers/gpu/drm/i915/gt/intel_engine_pm.c | 1 - > drivers/gpu/drm/i915/i915_active.c | 2 +- > drivers/gpu/drm/i915/i915_active.h | 2 +- > drivers/gpu/drm/i915/i915_request.c | 13 +- > drivers/gpu/drm/vmwgfx/vmwgfx_fence.c | 2 +- > include/linux/dma-fence.h | 26 ++++ > 9 files changed, 141 insertions(+), 70 deletions(-) > > -- > 2.34.1 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
