As I understand it, this is basically true triple-buffering implemented at the driver level for all games.
As far as the game is concerned, V-Sync is off, but the GPU will only present fully rendered frames to the display.
https://www.pcper.com/reviews/Graphics- ... mers/SLI-C
FastSync splits render and display pipelines
I sure hope you weren’t tried of technologies that end with “sync” because NVIDIA is releasing another one with the GTX 1080. FastSync is an alternative to Vsync On and Vsync Off states, but is not variable like G-Sync or FreeSync. The idea is straight forward: decouple the render pipe from the display pipe completely and there a lot of interesting things you can do. FastSync tells the game engine that Vsync is OFF, allowing it to render frames as fast as possible. The monitor is then sent frames at its maximum refresh rate but only completely rendered frames, avoiding the tearing artifacts usually associated with Vsync Off states.
FastSync creates a virtual buffer system that includes three locations. Front buffer, back buffer and the last rendered buffer. The front buffer is the one that is scanned out to the monitor at the same speed as the display refresh rate. The back buffer is the one that is being rendered to by the GPU and cannot be scanned out until it’s complete. The last rendered buffer will hold all new frames just completed in the back buffer, essentially saving a copy of the most recently rendered frame by the game. When the front buffer is finished scanning to the display, then the last rendered buffer would be copied to the front buffer and scanned out.
Interestingly, because buffer copies would take time and add latency, the buffers are just dynamically renamed. In high frame rate games the LRB and BB would switch positions concurrently at the render rate of the application, and when the FB had completed its most recent scan out, the current LRB would be renamed to the FB, immediately starting its scan out.
The usage model for FastSync is games that are running at very high frame rates (competitive gaming) and thus have to decide between the high input latency of Vsync On or the screen tearing of Vsync off. For CS:Go gamers that are used to hitting 200 FPS, you’ll be able to play the game tear-free with only a very slight increase in latency, about 8ms according to NVIDIA.
This is definitely something that should only be enabled in the NVIDIA Control Panel for those games that are running at frame rates well above the maximum refresh rate of your display. FastSync will be its very nature introduce some variability to the smoothness of your game, as it is “dropping” frames on purpose to keep you time with the refresh of your monitor while also not putting backpressure on the game engine to keep timings lined up. At high frame rates, this variability issue isn’t really an issue as the frame times are so high (200 FPS = 5ms) that +/- 5ms is the maximum frame to frame variance you would see. At lower frame rates, say 45 FPS, you could get as much as a 22ms variance.
FastSync is a cool new feature to improve the experience of FAST games, but don’t think NVIDIA has found a free alternative to variable refresh rate technology.
NVIDIA did state that FastSync was coming to Maxwell as well, and possibly even Kepler graphics cards.