Frame Rating Update – Why CrossFire was Omitted

Why are you not testing CrossFire??

One question I know will be asked about this review is that in our benchmarks today you will not see results from AMD CrossFire configurations in 2-Way or 3-Way combinations.  AMD is only represented by a single Radeon HD 7970 GHz Edition card while we are using both the GTX 690 dual-GPU card, GTX 680s in SLI and GTX TITANs in SLI. 

Why the bias?

If you haven't been following our sequence of stories that investigates a completely new testing methodology we are calling "frame rating", then you are really missing out.  (Part 1 is here, part 2 is here.)  The basic premise of Frame Rating is that the performance metrics that the industry is gathering using FRAPS are inaccurate in many cases and do not properly reflect the real-world gaming experience the user has.

Because of that, we are working on another method that uses high-end dual-link DVI capture equipment to directly record the raw output from the graphics card with an overlay technology that allows us to measure frame rates as they are presented on the screen, not as they are presented to the FRAPS software sub-system.  With these tools we can measure average frame rates, frame times and stutter, all in a way that reflects exactly what the viewer sees from the game.

We aren't ready to show our full sets of results yet (soon!) but the problems lie in that AMD's CrossFire technology shows severe performance degradations when viewed under the Frame Rating microscope that do not show up nearly as dramatically under FRAPS.  As such, I decided that it was simply irresponsible of me to present data to readers that I would then immediately refute on the final pages of this review – it would be a waste of time for the reader and people that skip only to the performance graphs wouldn't know our theory on why the results displayed were invalid.

Many other sites will use FRAPS, will use CrossFire, and there is nothing wrong with that at all.  They are simply presenting data that they believe to be true based on the tools at their disposal.  More data is always better. 

Here are these results and our discussion.  I decided to use the most popular game out today, Battlefield 3 and please keep in mind this is NOT the worst case scenario for AMD CrossFire in any way.  I tested the Radeon HD 7970 GHz Edition in single and CrossFire configurations as well as the GeForce GTX 680 and SLI.  To gather results I used two processes:

  1. Run FRAPS while running through a repeatable section and record frame rates and frame times for 60 seconds
  2. Run our Frame Rating capture system with a special overlay that allows us to measure frame rates and frame times with post processing.

Here is an example of what the overlay looks like in Battlefield 3.

Frame Rating capture on GeForce GTX 680s in SLI – Click to Enlarge

The column on the left is actually the visuals of an overlay that is applied to each and every frame of the game early in the rendering process.  A solid color is added to the PRESENT call (more details to come later) for each individual frame.  As you know, when you are playing a game, multiple frames will make it on any single 60 Hz cycle of your monitor and because of that you get a succession of colors on the left hand side.

By measuring the pixel height of those colored columns, and knowing the order in which they should appear beforehand, we can gather the same data that FRAPS does but our results are seen AFTER any driver optimizations and DX changes the game might make.

Frame Rating capture on Radeon HD 7970 CrossFire – Click to Enlarge

Here you see a very similar screenshot running on CrossFire.  Notice the thin silver band between the maroon and purple?  That is a complete frame according to FRAPS and most reviews.  Not to us – we think that frame rendered is almost useless. 

 

Data gathered from FRAPS

Here is a typical frame rate over time graph as generated by FRAPS.  Looks good right?  CrossFire and SLI are competitive with the advantage to the HD 7970s.

Data gathered from Frame Rating Capture

This is the same graph with data gathered from our method that omits RUNT frames that only represent pixels under a certain threshold (to be discussed later).  Removing the tiny slivers gives us a "perceived frame rate" that differs quite a bit – CrossFire doesn't look faster than a single card.

 

Data gathered from FRAPS – Click to Enlarge

This is the raw frame times as captured by FRAPS – again we are looking for a narrow band of frametimes to represent a smooth experience.  Both single cards do pretty well, but SLI sees a bit more variance and CrossFire sees a bigger one.  Quite a bit bigger.

Data gathered from Frame Rating Capture – Click to Enlarge

Here is the same data gathered by our new capture system – the CrossFire configuration looks MUCH worse with many frames hitting near 0ms of screen time.  That would be great if they were ALL like that but unfortunately they also scale up to 20ms and higher quite often.  Also notice NVIDIA's is actually MORE uniform indicating that there is some kind of smoothing going on after the frame leaves the game engine's hands. 

 

Data gathered from FRAPS – Click to Enlarge

Let's zoom in a bit – here is 100 frames of the FRAPS frametimes from above.  Notice the see-saw effect that the CrossFire output has…

Data gathered from Frame Rating Capture – Click to Enlarge

And see how much worse it is here in our Frame Rating Capture configuration.  The pattern is actually exaggerated on the CrossFire solution while the SLI configuration is smoother. 

 

Here are a couple more screenshots from our captures.

Frame Rating capture on Radeon HD 7970 CrossFire – Click to Enlarge

 

Frame Rating capture on GeForce GTX 680s in SLI – Click to Enlarge

 

Frame Rating capture on Radeon HD 7970 CrossFire – Click to Enlarge

 

Frame Rating capture on GeForce GTX 680s in SLI – Click to Enlarge

 

This is just a preview of what we have planned for our new Frame Rating Capture performance testing method.  We have gone through many games with this and the results can vary from looking better than FRAPS to looking much, much worse. 

I am eager to get your feedback – please feel free to leave comments below and the follow on to the conclusion of our GeForce GTX TITAN review!

« PreviousNext »