AMD Comments on GPU Stuttering, Offers Driver Roadmap & Perspective on Benchmarking
by Ryan Smith on March 26, 2013 2:28 AM ESTFinal Words
Bringing things to a close, when AMD first came to us about this, we had mixed feelings about what they were proposing. Typically, manufacturers only take issue with benchmarking methodologies when they have some deficiency on their part. Surprisingly enough, AMD's stance was equal parts recognition of where they had issues and offering their input on the right way to do things.
Meanwhile, we’ve wanted to do an article like this for some time now; specifically a dissection of FRAPS so that we could better explain why we have not been using FRAPS for investigating stuttering. To our surprise, we found AMD repeating many of the positions we held, and more importantly they were offering up further facts and additional data that we didn’t have access to that would help support our own position. So despite whatever AMD’s intentions were, this worked out well for us.
Ultimately AMD’s message has been one of information, explanation, and admission of oversight. AMD has been clear with us from the start that the primary reason they even ended up in this situation is because they weren’t doing sufficient competitive analysis, and that they have revised their driver development process so that they now do this analysis to prevent future problems. The fact that NVIDIA seemed to have figured all of this out much earlier was a point of frustration for AMD. The company likely left non-negligable amounts of performance on the table over the years, which could've definitely helped in close races.
At the same time they’ve been hard at work on fixing existing stuttering problems, with many of those fixes being delivered while fixes for more DX10+ games are right around the corner.
At the same time however AMD’s message is not just one about stuttering, but also one about benchmark and analysis methods with FRAPS. FRAPS, despite its limitations, has clearly exposed problems with AMD’s drivers that resulted in stuttering that AMD needed to fix. Meanwhile measuring frame intervals with FRAPS has become an increasingly common technique in reviews, only to really become popular at the same time as when AMD has finally fixed many of these issues.
AMD’s concern – and one that NVIDIA has shared with them in the past – is that measuring the rendering pipeline at the beginning of the pipeline like FRAPS goes about it does not accurately represent what the end user is seeing, due to the various buffers in the Pipeline and how the Present mechanism works. While FRAPS was good enough to pick up on the major stuttering issues in AMD’s drivers, as these issues get resolved it’s far too coarse a tool to pick up on finer issues, and in fact what FRAPS is now seeing is decoupled from what the user is seeing due to the presence of the context queue and other buffers. All of these, for the record, are points we agreed with AMD on, even before our meeting.
The end result of all of this is that change is in the air. Just as how quickly as Scott Wasson and others changed the nature of GPU reviewing by using FRAPS to measure frametimes, things must change again for GPU reviewers. If FRAPS is no longer an adequate tool to measure stuttering and frame intervals – as both AMD and NVIDIA insist – then new methods and new tools must be created to measure those factors at the end of the rendering pipeline, where the results would match what the end user is seeing. Though on the subject of tools, AMD for their part is favoring double-blind trials as the ultimate method of detecting stuttering. They’re fundamentally right since the perceptibility of stuttering depends on the person, but admittedly this is also the least objective/qualitative way of evaluating stuttering.
In any case, just as how change is in the air for GPU reviews, AMD has had to engage in their own changes too. They have changed how they develop their drivers, how they do competitive analysis, and how they look at stuttering and frame intervals in games. And they’re not done. They’re already working on changing how they do frame pacing for multi-GPU setups, and come July we’re going to have the chance to see the results of AMD’s latest efforts there.
For us this is what we hope to be the start of our own changes. There are tools in development that meet our criteria for better measuring frame intervals, and hopefully in the not too distant future we’ll be able to discuss those tools to a much greater degree, and to use those tools to go about measuring frame intervals in the manner we’ve always wanted to. But that is a story for another day, so until then you’ll have to stay tuned to find out.
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mi1stormilst - Tuesday, March 26, 2013 - link
All of us will benefit from the light shed on the subject with better testing and companies paying closer attention to issues and work arounds related to the subject. Still we would not even be talking about better testing methods right now without the attention it got from The Tech Report. I look forward to more sites implementing some type of real world testing methods that results in a true user experience evaluation. I reread the article and still standby my original conclusion. The Tech Report gets credit, but rather then stopping there this article seems to attack their methodology when they themselves had already admitted that it was less then perfect. To date there are still not better tools being used for reviews and The Tech Report still got the point across with what was available. I am a huge fan for what they did over there as I could not pinpoint why my AMD experience was less than optimal. It forced me to early retire my 6950 grab a very affordable 660 OC and enjoy a much smoother game experience. This is my first nVidia card since my trusty 4200ti and I am not looking back until AMD is on par with nVidia in the stuttering department...it was literally making me motion sick )-:SPBHM - Tuesday, March 26, 2013 - link
"holding back one frame but not another can sometimes make the frame display evenly, but from a simulation step only a few milliseconds after the previous step"wouldn't this also happen with the single GPU "heartbeat stuttering"?
BrightCandle - Tuesday, March 26, 2013 - link
Yes it would, which is exactly the problem with the heartbeat pattern that AMD's problem causes. You can deliver the frames evenly out to the monitor but their contents has a noticeable stutter due to the graphics driver accepting the frames unevenly. The heartbeat is a sign of a real problem without a doubt, all non smooth frame time captures are. What they are not is a sign that the DVI monitor is seeing frames at those periods, but then no one ever said that was what was being measured anyway.The best way to think about it is that this is the problem going into the pipeline, measuring the output also needs to be done to get the smoothness on the output. Only with both can you understand the impact. We have half the picture, and that half is accurately measured by fraps.
Gunbuster - Tuesday, March 26, 2013 - link
Design and launch a product. Ignore user feedback.Did we forget about those people with $2000 laptops sporting AMD mobile card drivers that didn't work correctly for over a year due to some bug with the graphics switching MUX? This seems to be a pattern that revolves around AMD software people being wholly out of their depth, overworked, or just not caring. They don’t even seem to be able to figure out when they have a fix. The laptop GPU story here on AT was presented as AMD sending over beta drives and asking “Did we fix it this time?”
rootheday - Tuesday, March 26, 2013 - link
One minor correction to the description of the submission of commands through the stack - the DirectX runtime under Windows Vista and later does NOT accumulate a frames' worth of draw calls before sending them to the UMD. I believe it sends state and draw calls to the UMD immediately.The UMD accumulates commands in the command buffer and flushes them to the KMD either when a present call occurs, when the command buffer is full, or when the application requests to read back the results of enqueued rendering (Map/Lock/read Query result).
It used to be true under Windows XP that the dx runtime accumulated calls and dispatched them to the driver - but that is because in XP, the driver ran in kernel mode and it was too expensive to make the user mode->kernel mode transition on every "SetState", etc call.
tynopik - Tuesday, March 26, 2013 - link
"frame latter than it would have" -> later (pg 3)cactusdog - Tuesday, March 26, 2013 - link
As a long time ATI/AMD fan this report doesn't fill me with confidence. It appears AMD is using anandtech for their public relations spin on the stuttering issue. I don't blame anandtech for running the story, AMD's comments are newsworthy and anandtech deserves credit for being honest about AMD's intentions. On the negative side, the explanation about fraps not being an effective tool only need to be said once, it seems (by the number of times it was mentioned) that AMD's message is to make sure everyone knows Fraps its not accurate, but doesn't explain why Nvidia performs better.On the issue, it sounds like AMD is conceding and preparing us for much of the same. No where in the explanation do they mention why Nvidia performs better in the latency tests, other than to say its not what the end user is seeing. Well I disagree, users have been complaining about stuttering for years. I just don't believe that AMD have never looked into this issue before. Also with the multi-gpu stuttering. It has been an issue since crossfire/SLI first appeared and nothing has really happened there.
Im a fan of AMD cards but I use both brands and personally I have noticed Nvidia do a better job with latency and general responsiveness in game, whereas ATI/AMD has the edge with image quality. Its subtle, and probably not something the average user notices but a lot of people do notice.. If AMD can solve this issue they would sell many more cards but by the sounds of this article, its too big and complex for them to solve completely without major work. Hence the excuses. Nvidia has to play by the same rules, the same OS etc and they do a better job at latency/stuttering, hopefully AMD can fix it enough to at least perform as good as a NVidia card.
WaltC - Tuesday, March 26, 2013 - link
"NVIDIA made a big deal about moving away from timedemos and average frame rates during the early GeForce FX (NV30) days, when its cards might have delivered a decent gaming experience but were slaughtered in most benchmarks."Well, that's not really what happened at all...;) The chip "slaughtering" everything nVidia made in those days was the ATi R300. Seems rather strange to tell just half of that story. And the problem nVidia had with benchmarks wasn't technical--it was that nVidia was found to be actively cheating in 3dMark (camera on rails), among other cheats/shortcuts/optimizations in their drivers. The benchmarks told a story nVidia couldn't abide, and that was how much better the R300 was than anything nVidia had at the time. R300 was in every sense a revolution in the 3d gpu markets, blowing everything else away. All gpus on the market today are descended from R300 (just as all Intel and AMD x86 cpus are descended from AMD's original 64-bit Opterons.) nVidia did eventually own up to all of it, right before cancelling the nV30 after a month or two in production, however. People kept publishing proof after proof of what nVidia was doing until finally the company said "uncle." nVidia has been a better company since, imo. At least, its products are certainly better.
I'm using a single ATi gpu and over the last few years I have to say that I haven't seen any stuttering worth mentioning. Whenever I have seen stuttering it is usually due to some software condition or other, and rectified by the appropriate patch. I do appreciate your pointing out that Fraps isn't perfect and I think TR should stop pretending that it is. Fraps as you point out was never intended to measure this kind of latency and so using it to produce data other than frame-rate data is an "off-label" use of the program, imo. And also as you point out, I use vsync more often than not.
Really, though, I would loathe seeing AMD optimizing its drivers just to look better in TR's off-label Fraps usage...!...;) Let's hope that doesn't happen as I got quite a belly full of that sort of thing back in the nV30 days--enough to last me a lifetime.
beginner99 - Tuesday, March 26, 2013 - link
How can FRAPS detect any vendor-specific stuttering if it injects itself before the gpu-driver is called?The second thing is that v-sync is just crap. I'm not a professional gamer, not even close but in certain games turning it off made me a much better player and the difference is huge. even more annoyingly it was not directly noticeable. I did not "feel" anything changed. Except that my stats were better. Tearing and stuttering: no issue for me so far.
DanNeely - Tuesday, March 26, 2013 - link
The timing at the point it's measuring is normally blocked until the queue the GPUs feeding from has an open slot?