Demystifying Graphics and Media Work Synchronisation
summary
Explains how current Linux graphics relies on DRM and Mesa and that buffer sharing via dma-buf and completion via dma-fence fd already work in production but are not allocators and force kernel stalls for implicit sync; shows that newer kernel-level primitives like timeline semaphores add integer-valued semaphores and permit weight-before-signal which can leave fences unsignaled and break prior guarantees; describes a hybrid approach being prototyped and an implemented compositor pattern (adaptive compositor gating in Mutter/GNOME) that reduces 16 ms frame jitter by checking fence retirement just before display deadlines.
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chapters (34)
- 0:00Introduction
- 0:27Outline
- 1:07DM
- 1:57Device Specific Operations
- 4:43Memory Allocation
- 5:55Command Submission
- 7:02Access
- 7:29User Space
- 8:37Implicit synchronization
- 12:59Bo Buff Limitations
- 13:33Bo Buff Universal Exchange
- 14:05Sync Operations
- 14:48Portable Cross Device
- 15:42Kernel
- 17:16DNA Reservation
- 18:52Why
- 19:39Timeline
- 21:58Sync Objects
- 23:30Weight Before Signal
- 25:36Memory Management
- 30:29Games
- 31:00GPU and Compute
- 32:22All the answers
- 34:45Performance penalty
- 35:38Design outline
- 36:04Display
- 36:50Timing
- 38:59VBlank
- 39:14Latency
- 40:00Debug
- 40:55Latency Reduction
- 41:11Adaptive Synchronisation
- 43:50Graphics Difficulty
- 44:05Uncanny Valley
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