Tear Reduction/Smooth (A)Sync
Overview
- introduced to smoothly transition between old and new frame during an async flip.
- It uses both blending and dithering to achieve this.
- Can be exposed as a CRTC property.
Different levels of smoothening
- Smooth Sync disabled
-4.png)
- Level 1
-2.png)
- Level 2
-1.png)
- Level 3
-4.png)
- Level 4
-3.png)
- Level 5
-0.png)
Performance penalty
Enabling Smooth Sync reduces async flip throughput. The higher the level, the greater the performance cost.
Test: kms_async_flips --r async-flip-speed-test on Wildcat Lake (Linux 6.19.0-rc4) on an HD display
| Subtest | Baseline (flips/vblank) | Level 1 (flips/vblank) | Level 5 (flips/vblank) |
|---|---|---|---|
| pipe-A-eDP-1-4 | 6537 | 3109 | 713 |
| pipe-B-eDP-1-4 | 6600 | 2543 | 712 |
| pipe-C-eDP-1-4 | 6538 | 3177 | 713 |
At level 1 the flip count drops to ~50% and at level 5 it drops to ~10% of the baseline.