DMA-Fence Deadline Awareness Proposed To Help Ensure GPU Drivers Render On-Time

There is the phenomenon on Linux where when double-buffered rendering and missing vblanks can lead to the GPU running at a lower frequency when instead the opposite should happen so it will try to not miss vblanks in the first place. In the past there's been talks of "boost" support in the GPU drivers or also workarounds from user-space like dynamic triple buffering, but sent out this week is a new proposal around DMA-Fence deadline awareness as another means of addressing this problem.

DMA-Fence deadline awareness is about being able to set a desired deadline on a fence for when the waiter would like to see the fence signaled. With the use-case being pursued, the deadline would be set as the next vblank time. Over earlier approaches this deadline awareness method should work out better in the context of atomic helpers and where the display and GPU drivers are different.

This patch series introduces the notion of DMA-Fence deadline awareness and also makes the changes to the DRM scheduler and for being able to get the next vblank time. The current patches though aren't yet wired into any of the actual Direct Rendering Manager drivers.

This deadline awareness is being worked on by Google's Rob Clark and he is currently wiring up the support to work with at least the MSM DRM (Qualcomm Adreno) driver. We'll see where this DMA-Fence deadline awareness work leads.