Multi-GPU - (FCAT) Frametime experience
Frametime and latency performance
With FCAT we will look into Frame Experience Analysis. Basically with the charts shown we are trying to show you graphics anomalies like stutters and glitches in a plotted chart. Lately there has been a new measurement introduced, latency measurements. Basically it is the opposite of FPS.
- FPS mostly measures performance, the number of frames rendered per passing second.
- Frametime AKA Frame Experience recordings mostly measures and exposes anomalies - here we look at how long it takes to render one frame. Measure that chronologically and you can see anomalies like peaks and dips in a plotted chart, indicating something could be off.
We have a detailed article (read here) on the new FCAT methodology used, and it also explains why we do not use FRAPS anymore. Frametime - Basically the time it takes to render one frame can be monitored and tagged with a number, this is latency. One frame can take say 17 ms. Higher latency can indicate a slow framerate, and weird latency spikes indicate a stutter, jitter, twitches; basically anomalies that are visible on your monitor.
What Do These Measurements Show?
What these measurements show are anomalies like small glitches and stutters that you can sometimes (and please do read that well, sometimes) see on screen. Below I'd like to run through a couple of titles with you. Bear in mind that Average FPS often matters more than frametime measurements.
FPS plot - Multi GPU
Above framerates relative to percentiles. Basically we take all recorded 1800 frames, make a data-set out of it and place them in a relative chart towards FPS. At 50% you would be looking at your average framerates as measured with FCAT. Higher is better. We measure at Quad HD (2560x1440) as we are tied to the DVI output connector with FCAT. At Ultra HD the Radeon R9 Fury CFX would be at the top. Let's move on-wards to frame-times (latency measurements) though as we need to look at some shocking stuff (literally).
Above an example recording of FCAT frames being captured, this is the GTX 980 (Single card) at work in the first 31 seconds of the benchmark.
Frame Pacing / Frametime - Multi GPU
Above a plotted frame-time results of the test run @ 2560x1440 performed with a Radeon R9 Fury (4GB) in 2560x1440 (WQHD) both single and in Crossfire. The game is a visible mess with flickering and stutters up-to the point that it is unplayable, FCAT backs that visual observation up. This could be easily interpreted as micro-stuttering, but there's something else really wrong here. For proper Multi-GPU support we'll need a driver fix from AMD, newer than then Crimson 16.2.1 driver. Until then I recommend you to run just one GPU (if you are experiencing this issue). Nvidia then, have a look below:
Here we use a GeForce GTX 980 at 2560x1440 single & SLI. This test run lasts roughly 30 seconds and is based on the first 31 seconds of the benchmark. Frame pacing looks to be more uniform with SLI over Crossfire, but as you can see ... that's the classic definition of micro-stuttering and if we look at the screen, we can see there's weird stuff going on, yet it remains playable and a novice might not even notice it.
In the output chart above we combined all results from the single and 2-way Multi-GPU cards. Again this is 2560x1440, at 3840x2160 the Fury CFX combo would have been in the lead. Multi-GPU for both vendors at this first day launch is I'm afraid far from optimal.