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Frame Rating Dissected: Full Details on Capture-based Graphics Performance Testing

How Games Work

 

Because of the complexity and sheer amount of data we have gathered using our Frame Rating performance methodology, we are breaking it up into several articles that each feature different GPU comparisons.  Here is the schedule:

 

Introduction

The process of testing games and graphics has been evolving even longer than I have been a part of the industry: 14+ years at this point. That transformation in benchmarking has been accelerating for the last 12 months. Typical benchmarks test some hardware against some software and look at the average frame rate which can be achieved. While access to frame time has been around for nearly the full life of FRAPS, it took an article from Scott Wasson at the Tech Report to really get the ball moving and investigate how each frame contributes to the actual user experience. I immediately began research into testing actual performance perceived by the user, including the "microstutter" reported by many in PC gaming, and pondered how we might be able to test for this criteria even more accurately.

The result of that research is being fully unveiled today in what we are calling Frame Rating – a completely new way of measuring and validating gaming performance.

The release of this story for me is like the final stop on a journey that has lasted nearly a complete calendar year.  I began to release bits and pieces of this methodology starting on January 3rd with a video and short article that described our capture hardware and the benefits that directly capturing the output from a graphics card would bring to GPU evaluation.  After returning from CES later in January, I posted another short video and article that showcased some of the captured video and stepping through a recorded file frame by frame to show readers how capture could help us detect and measure stutter and frame time variance. 

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Finally, during the launch of the NVIDIA GeForce GTX Titan graphics card, I released the first results from our Frame Rating system and discussed how certain card combinations, in this case CrossFire against SLI, could drastically differ in perceived frame rates and performance while giving very similar average frame rates.  This article got a lot more attention than the previous entries and that was expected – this method doesn’t attempt to dismiss other testing options but it is going to be pretty disruptive.  I think the remainder of this article will prove that. 

Today we are finally giving you all the details on Frame Rating; how we do it, what we learned and how you should interpret the results that we are providing.  I warn you up front though that this is not an easy discussion and while I am doing my best to explain things completely, there are going to be more questions going forward and I want to see them all!  There is still much to do regarding graphics performance testing, even after Frame Rating becomes more common. We feel that the continued dialogue with readers, game developers and hardware designers is necessary to get it right.

Below is our full video that features the Frame Rating process, some example results and some discussion on what it all means going forward.  I encourage everyone to watch it but you will definitely need the written portion here to fully understand this transition in testing methods.  Subscribe to your YouTube channel if you haven't already!

Continue reading our analysis of the new Frame Rating performance testing methodology!!

How Games Work

Before we dive into why I feel that our new Frame Rating testing method is the best for the gamer, there is some necessary background information that you must understand.  While we all play games on a near daily basis, most of us don’t fully grasp the complexity and detail that goes into producing an image that makes its way from code a developer writes to the pixels on your monitor.  The below diagram attempts to simplify the entire process from the game engine to the display.

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In the image above we have defined a few important variables based on time that will help us explain graphics anomalies.  The first is t_game and it refers the internal time that the game engine is using to keep track of its internal simulations and interactions.  This is where processes like the physics simulations, user interface, artificial intelligence and more are handled.  Different game engines keep time in different ways, but they usually fall into two categories: fixed or variable time steps.  In a fixed time method the game engine cycles the environment in its internal simulation on a regular, fixed iteration.  This is more predictable but it also forces other systems to sync up to it (drivers, GPU rendering) which may cause some issues.  The variable time step method allows a lot more flexibility, but it can be more complicated for developers to maintain a fluid feeling simulation because of simply not knowing when the next simulation update will take place. 

Following that is t_present, the point at which the game engine and graphics card communicate to say that they are ready to pass information for the next frame to be rendered and displayed.  What is important about this time location is that this is where FRAPS gets its time stamps and data and also where the overlay that we use for our Frame Rating method is inserted.  What you should notice right away though is that there is quite a bit more work that occurs AFTER the t_present command is sent and before the user actually sees any result.  This in particular is where capture method’s advantages stem from.  

After DirectX calls the game engine to recieve its time, the graphics driver gets its hands on it for the first time.  The driver maps the DX calls to its own specific hardware and then starts the rendering process on a GPU.  Once the frame is rendered, we will define another variable, t_render, which is reported when the image is ready to be sent to a display.  Finally, t_display will be defined as the time in which data from the frame is on the display, whether that be a complete frame (Vsync enabled for example) or a partial frame. 

You can likely already see where the differences between FRAPS data measurement and Frame Rating measurement start to develop.  Using capture hardware and analysis tools that we’ll detail later, we are recording the output from the graphics card directly as if it were a monitor.  We are essentially measuring frames at the t_display level rather than the t_present point, giving us data that has been filtered through the entire game engine, DirectX, driver, rendering and display process. 

It is also useful to discuss stutter and how it relates to these time definitions.  Despite some readers opinions, stutter in game play is related to the smoothness of animation and not hard wired to low frame rate.  If you have a steady frame rate of 25 FPS you can still have an enjoyable experience (as evident by the 24 FPS movies we all watch at the theater).  Instead, we should view stutter as a variance level between t_game and t_display; if the total display time runs at 50ms (20 FPS) you won’t have stuttering in animation (in most cases) but if total display time shifts between 20ms and 50ms you definitely will.

In our second video on Frame Rating, we looked at a capture from Dishonored in a frame by frame analysis and saw a rather large stutter.  I think a better term for that is a hitch, a large single frame rate issue that isn’t indicative of a microstutter smoothness problem.  Using the above variables, a hitch would be a single large instance of t_game – t_display.  As you’ll see in our results analysis pages (including games like Skyrim) this happens fairly often, even in some games that are smooth otherwise. 

Our 2nd video on Frame Rating from a couple months ago...

There is also a completely different discussion on the advantages and differences of capturing data from FRAPS versus capturing data with our Frame Rating methodology.  I believe that the advantages of hardware capture outweigh the concerns currently, but in reality the data that FRAPS generates isn’t that important, it just happens to be the closest data point to another metric we would love to know more about: game time. 

Game time is the internal game clock that the software engine uses to keep track of the physical world.  This clock could be based on a fixed time span for each tick or it could be variable or timed off of another source (like the OS or GPU driver).  An Intel GPU engineer, Andrew Lauritzen, recently made a great post over on the Beyond3D.com forums about game time, back pressure on the game pipeline and much more.  Here is a short portion of that post, but I would encourage everyone to read the entirety completely:

1) Smooth motion is achieved by having a consistent throughput of frames all the way from the game to the display.

2) Games measure the throughput of the pipeline via timing the back-pressure on the submission queue. The number they use to update their simulations is effectively what FRAPS measures as well.

3) A spike anywhere in the pipeline will cause the game to adjust the simulation time, which is pretty much guaranteed to produce jittery output. This is true even if frame delivery to the display (i.e. rendering pipeline output) remains buffered and consistent. i.e. it is never okay to see spikey output in frame latency graphs.

4) The converse is actually not true: seeing smooth FRAPS numbers does not guarantee you will see smooth display, as the pipeline could be producing output to the display at jittery intervals even if the input is consistent. This is far less likely though since GPUs typically do relatively simple, predictable work.

Clearly the best case for evaluating overall gaming performance will be to have access to the internal game and measure it in comparison the output from Frame Rating, the actual frames on your display.  Differences there could be analyzed to find exact bottlenecks in the pipeline from game code to display.  The problem is no game engine developers allow access to the information currently and the number of different engines in use today makes it difficult for even the likes of NVIDIA and AMD to gather data reliably.  There is opportunity for change here if an API were to exist (in DirectX for example) that would give all game engines reliable time iterations that we would then have access to.

 

NVIDIA's Involvement

You may notice that there is a lot of “my” and “our” in this story while also seeing similar results from other websites being released today.  While we have done more than a year’s worth of the testing and development on our own tools to help expedite a lot of this time consuming testing, some of the code base and applications were developed with NVIDIA and thus were distributed to other editors recently.

NVIDIA was responsible for developing the color overlay that sits between the game and DirectX (in the same location of the pipeline as FRAPS essentially) as well as the software extractor that reads the captured video file to generate raw information about the lengths of those bars in an XLS file.  Obviously, NVIDIA has a lot to gain from this particular testing methodology: its SLI technology looks much better than AMD’s CrossFire when viewed in this light, highlighting the advantages that SLI’s hardware frame metering bring to the table. 

The next question from our readers should then be: are there questions about the programs used for this purpose?  After having access to the source code and applications for more than 12 months I can only say that I have parsed through it all innumerable times and I have found nothing that NVIDIA has done that is disingenuous.  Even better, we are going to be sharing all of our code from the Perl-based parsing scripts (that generate the data in the graphs you’ll see later from the source XLS file) as well as a couple of examples of the output XLS files. 

Not only do we NEED to have these tools vetted by other editors, but we also depend on the community to keep us on our toes as well.  When we originally talked with NVIDIA about this project the mindset from the beginning was merely to get the ball rolling and let the open source community and enthusiast gamers look at every aspect of the performance measurement.  That is still the goal – with only one minor exception: NVIDIA doesn’t want the source code of the overlay to leak out simply because of some potential patent/liability concerns.  Instead, we are hoping to have ANOTHER application built to act as the overlay; it may be something that Beepa and the FRAPS team can help us with.

March 30, 2013 | 05:47 PM - Posted by bystander (not verified)

I have a hard time trying to grasp exactly how erratic input would affect the results. I have a feeling, based on my constitution (I get simulator sickness with poor latency), that the best case is which ever has the lowest worst case interval times.

March 30, 2013 | 10:55 PM - Posted by bystander (not verified)

..But then you have occasional latency increases. Of course those increases are to remove redundant frames, and once increased, they probably don't need much adjustments most the time.

This whole topic always gets me going back and forth, but my instincts is overall, even if latency is considered, even spacing matters more as it adds more useful points of input, assuming it adds only marginal/occasional increases of latency.

March 28, 2013 | 05:20 PM - Posted by Bob Jones (not verified)

Can you address the visual quality differences between the two cards? Specifically on Sleeping Dogs, the 660 Ti seems to be missing some lighting sources outside - most noticeable is the cafe/shop lights before you go down the stairs, and then the store across the street right at the end of the vieo.

March 29, 2013 | 07:46 AM - Posted by Ryan Shrout

Time of day in the game when those videos were recorded?  They should be basically identical, I'll check.

March 29, 2013 | 12:10 AM - Posted by I don't have a name. (not verified)

Fascinating article. I think it'll take a few reads to fully comprehend everything that is being said. Thank you indeed, I found it fascinating. Certainly, as a 7970 owner, I'll be holding off on a potential second 7970 purchase for the time being.

March 29, 2013 | 02:09 AM - Posted by rezes (not verified)

The last GeForce 314.22 Beta Drivers and last Radeon drivers 13.3 beta 3. Please using these drivers on yours test.

AMD driver may be more stable on this drivers!

March 29, 2013 | 07:46 AM - Posted by Ryan Shrout

Nothing has changed on the issues in question.

March 29, 2013 | 02:15 AM - Posted by technogiant (not verified)

Thanks for the great article and all the work you've done guys.

I run 2x gtx 460's is sli and while I dislike screen tearing I've noticed that options such as vsync, active vsyn and frame rate limiters actually make the experience less smooth as appears to have been highlighted in this article.

I've considered getting a 120Hz monitor just so I can run without any of those options at a decent frame rate but use sufficiently high settings so as not to go above 120Hz and so incur screen tearing.

Thinking further I'd like Nvidia to develop a variation of their gpu boost technology that would actually down clock the gpu to prevent frame rates from exceeding the monitors refresh rate.....think this would give the benefits of no screen tearing without the negatives of vsync and the like.

Thanks again for the article guys.

March 29, 2013 | 02:37 AM - Posted by technogiant (not verified)

Actually using gpu boost dynamically to both under and overclock the gpu to achieve a target frame rate could be a very nice way of producing a smoothed experience without any of the negatives of other methods as its occurring directly at the gpu instead of in the game engine to display time line.

March 29, 2013 | 05:01 AM - Posted by Pick23 (not verified)

So is this article saying that even with the new testing methodologies:
1.Single card 7970ghz is still slightly better than the 680
2.Crossfire absolutely sucks
?

March 29, 2013 | 05:18 AM - Posted by John Doe (not verified)

7970 Ghz is slightly better than a 680 ONLY at stock.

When you're comparing 7970 Ghz to 680, things ENTIRELY depend on clock speeds since the 7970 Ghz is nothing more than a pre-OC'ed 7970.

But yes, CF does indeed sorta suck. Still.

March 29, 2013 | 04:26 PM - Posted by Anonymous (not verified)

Sweet 7970 still the best card under.. well under $1000 lol

March 30, 2013 | 06:21 PM - Posted by steen (not verified)

What's stock for a 680? ;) 7970 GE is slightly slower than Titan...

CF sucks just like SLI. What's your poison, input lag or frame metering? Do poeple understand what "runts" are? CF is actually rendering the frames, you just don't benefit as they're too close together. One frame renders the top 1/4 of the screen when the next frame starts. Your top ~200 lines are the fastest on your screen. ;)

(Sorry for the previous multi-posts. Don't know what happened there.)

April 7, 2013 | 10:15 AM - Posted by John Doe (not verified)

I have ran far more CF and SLi setups than you did FOR YEARS and understand far more abouts these things than you and your little silly mind does.

March 29, 2013 | 08:39 AM - Posted by fausto412 (not verified)

interesting piece, good job pcper.com

now I wonder if when AMD does a global fix my 6990 performance will be dramatically improved on bf3?

and what is the effect of correcting this to latency and actual framerate? will we see FPS go down at the expense of frametimes?

It is Obvious Nvidia was on top of this for some time...I just don't see a proper fix in 120 days.

March 29, 2013 | 09:24 AM - Posted by Chad Wilson (not verified)

Just out of scientific curiosity, did you do a run without the splitter in the mix to confirm that the splitter is not adding any latency to your tests?

March 29, 2013 | 09:33 AM - Posted by Anonymous (not verified)

Do people actually use vsync without some form of triple buffering?

I don't see how. Jumping between 30 and 60fps or whatever is not an enjoyable, nor smooth experience.

So, if you can enable vsync AND allow the game to sweep through a normal range of available framerates, does this negate the increased frame times of constantly switching back and forth between high fps and low fps?

March 29, 2013 | 09:56 PM - Posted by bystander (not verified)

V-sync, even with triple buffering, still jumps back and forth between 16ms and 33ms, but it does it between frames. A 120hz monitor helps here, as you can have 25ms frames too, so it is less of a variance.

March 29, 2013 | 09:36 AM - Posted by Anonymous (not verified)

Furthermore, is playing a game without vsync enabled REALLY an option?

Are you sure gamers all over the world disable it to be rid of the latency issues? I'm not so sure.

I'll happily take a little latency in a heated round of counter-strike than end up dead, or missing my shot because 50% of the screen shifted 8 feet to the right. (screen tearing).

Pretty much all games are unplayable without the use of vsync and I'm not convinced it's a personal preference, either, if you enjoy your experience while you're tearing frames - I'd just call you a mean name that insinuates you're not telling the truth.

March 29, 2013 | 11:00 AM - Posted by Marty (not verified)

If you are a competitive player, VSync is not an option, you are lagging an extra frame behind.

March 29, 2013 | 09:45 AM - Posted by rezes

Where is the new tests? and when?

March 29, 2013 | 11:20 AM - Posted by Anonymous (not verified)

So how much did nVidia pay you?

While I can see the potential in this kind of testing, and some of the issues you have mentioned are valid, you have drawn quite a bold and one sided conclusion using the competitor's software. I'll save my judgements for when this becomes open source.

March 29, 2013 | 05:12 PM - Posted by Fergdog (not verified)

It's not purely Nvidia made software, if you read the article or paid attention to this site you'd know Ryan co-developed this benchmark with Nvidia and he's been working on it for a long time.

April 2, 2013 | 08:10 PM - Posted by Anonymous (not verified)

nVidia has to do almost everything, the amd fans need to get used to it.

AMD's years long broken bottom line and years of massive layoffs and closings mean they claim they "weren't even aware of this issue !? !! "

- like every other total screw up AMD gets caught on with their dragon drawers on the floor next to their spider platform, buck naked in epic fail and presumably clueless...

Maybe we need some depositions and subpoenas of internal emails to see just how much they covered up their epic fail here.

March 29, 2013 | 05:00 PM - Posted by Fergdog (not verified)

Quick question, for adaptive vsync, you put it on half refresh rate didnt you?

March 29, 2013 | 05:02 PM - Posted by Fergdog (not verified)

Half refresh adaptive only really makes sense on 120hz monitors, not sure why you used that setting on a 60hz monitor for benchmarking.

March 29, 2013 | 08:06 PM - Posted by Anonymous (not verified)

Hoping you post the titan and and info today as promised!!!!!!!!!

March 29, 2013 | 08:07 PM - Posted by Anonymous (not verified)

Titan and amd

March 29, 2013 | 09:56 PM - Posted by MaxBV (not verified)

Waiting on that GTX 690 and Titan article still, hope you guys haven't forgotten.

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