AMD Frame Pacing Explored: Catalyst 13.8 Brings Consistency to Crossfire
by Ryan Smith on August 1, 2013 2:00 PM ESTTotal War: Shogun 2
Our first detailed benchmark is Shogun 2, which is a continuing favorite to our benchmark suite. Total War: Shogun 2 is the latest installment of the long-running Total War series of turn based strategy games, and alongside Civilization V is notable for just how many units it can put on a screen at once. Even 2 years after its release it’s still a very punishing game at its highest settings due to the amount of shading and memory those units require.
For the sake of completeness we’re posting our frame rate charts for each of our individual games, but in general there’s nothing here we haven’t seen before in the 7990 review, in other reviews, or in Bench. The 7990 and GTX 690 still swap places fairly regularly.
Looking at our expanded delta percentages for Shogun, we can see how the 7990 and other Crossfire solutions stack up to the GTX 690 and other SLI solutions. For all AFR configurations the results match what we saw in our summary, with NVIDIA’s solutions offering lower deltas than AMD’s even with the new drivers.
This is actually AMD’s weakest game, with both the 7970GECF and 7990 exceeding 20% variability on this game. However it’s also the only non-action game in this collection, so it’s the game least affected by higher levels of variation and consequently the game AMD can afford to do the worst at. Nevertheless the improvement over Catalyst 13.6 without frame pacing is nothing short of amazing.
Meanwhile we’ll hit upon this a few times, but as a reminder AMD’s frame pacing improvements apply to older cards too, so the 6990 has its frame pacing problems resolved like the rest of AMD’s multi-GPU cards. It actually does better than the rest, we believe due to the fact that the lower framerate and higher frame times give AMD’s drivers more time to analyze and schedule frames.
Looking at the FCAT graphs, we can see that the higher variability of the 7990’s frame times is represented well. Though NVIDIA’s frame time spikes are more extreme than AMD’s.
Finally we have our 95th percentile frame times. Despite the fact that AMD’s framerates are down slightly versus Catalyst 13.6, their 95% percentile times are way up. Simply by instituting frame pacing they’ve dropped from 36.2ms to 21.5ms per frame.
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chizow - Friday, August 2, 2013 - link
That makes sense, but I guess the bigger concern from the outset was how AMD's allowance of runtframes/microstutter in an "all out performance" mentality might have overstated their performance. You found in your review that AMD performance typically dropped 5-10% as a result of this fix, that should certainly be considered, especially if AMD isn't doing a good job of making sure they implement this frame time fix across all their drivers, games, APIs etc.Also, any word whether this is a driver-level fix or an game-specific profile optimization (like CF, SLI, AA profiles)?
Ryan Smith - Friday, August 2, 2013 - link
The performance aspect is a bit weird. To be honest I'm not sure why performance was up with Cat 13.6 in the first place. For a mature platform like Tahiti it's unusual.As for the fix, AMD has always presented it as being a driver level fix. Now there are still individual game-level optimizations - AMD is currently trying to do something about Far Cry 3's generally terrible consistency, for example (an act I'm convinced is equivalent to parting the Red Sea) - but the basic frame pacing mechanism is universal.
Thanny - Thursday, August 1, 2013 - link
Perhaps this will be the end of the ludicrous "runt" frame concept.All frames with vsync disabled are runts, since they are never completely displayed. With a sufficiently fast graphics card and/or sufficiently less complex game, every frame will be a runt even by the arbitrary definitions you find at sites like this.
And all the while, nothing at all is ever said about the most hideous artifact of all - screen tearing.
Asik - Thursday, August 1, 2013 - link
There is a simple and definite fix for tearing artifacts and you mention it yourself - vsync. If screen tearing bothers you, and I think it should bother most people, you should keep vsync on at all times.chizow - Thursday, August 1, 2013 - link
Vsync or frame limiters are certainly workarounds, but it also introduces input lag and largely negates the benefit of having multiple powerful GPUs to begin with. A 120Hz monitor would increase the headroom for Vsync, but also by nature reduces the need for Vsync (there's much less tearing).krutou - Friday, August 2, 2013 - link
Triple buffering solves tearing without introducing significant input lag. VSync is essentially triple buffering + frame limiter + timing funny business.I have a feeling that Nvidia's implementation of VSync might actually not have input lag due to their frame metering technology.
Relevant: http://www.anandtech.com/show/2794/3
chizow - Saturday, August 3, 2013 - link
Yes this is certainly true, when I was on 60Hz I would always enable Triple Buffering when available, however, TB isn't the norm and few games implemented it natively. Even fewer implemented it correctly, most use a 3 frame render ahead queue, similar to the Nvidia driver forcing it which is essentially a driver hack for DX.Having said all that, TB does still have some input lag even at 120Hz even with Nvidia Vsync compared to 120Hz without Vsync (my preferred method of gaming now when not using 3D).
vegemeister - Monday, August 5, 2013 - link
The amount of tearing is independent the refresh rate of your monitor. If you have vsync off, every frame rendered creates a tear line. If you are drawing frames at 80Hz without vsync, you are going to see a tear every 1/80 of a second no matter what the refresh rate of your screen is. The only difference is that a 60Hz screen would occasionally have two tear lines on screen at once.chizow - Thursday, August 1, 2013 - link
Sorry, not even remotely close to true. Runt frames were literally tiny shreds of frames followed by full frames, unlike normal screen tearing with Vsync off that results in 1/3 or more of the frame being updated at a time, consistently.The difference is, one method does provide the impression of fluidity and change from one frame to the next (with palpable tearing) whereas runt frames are literally worthless unless you think 3-4 rows worth of image followed by full images provides any meaningful sense of motion.
I do love the term "runt frame" though, an anachronism in the tech world born of AMD's ineptitude with regard to CrossFire. I for one will miss it.
Thanny - Thursday, August 1, 2013 - link
You're not making sense. All frames with vsync off are partial. The frame buffer is replaced in the middle of screen updates, so no rendered frame is ever displayed completely.A sense of motion is achieved by displaying different frames in a time sequence. It has nothing to do with showing parts of different frames in the same screen refresh.
And vsync adds a maximum latency of the inverse of the screen refresh (16.67ms for a 60Hz display). On average, it will be half that. If you have a very laggy monitor (Overdrive-TN, PVA, or MVA panel types), that tiny bump from vsync might push the display lag to noticeability. For plain TN and IPS panels (not to mention CRT), there will be no detectable display lag with vsync on.