Review Index:
Feedback

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

Vsync and its Effect on Frame Rating – Does it fix CrossFire?

After publishing the Frame Rating Part 3 story, I started to see quite a bit of feedback from readers and other enthusiasts with many requests for information about Vsync and how it might affect the results we are seeing here.  Vertical Sync is the fix for screen tearing, a common artifact seen in gaming (and other mediums) when the frame rendering rate doesn’t match the display’s refresh rate.  Enabling Vsync will force the rendering engine to only display and switch frames in the buffer to match the vertical refresh rate of the monitor or a divisor of it.  So a 60 Hz monitor could only display frames at 16ms (60 FPS), 33ms (30 FPS), 50ms (20 FPS), and so on with a 120 Hz monitor could also being capable of 8ms (120 FPS), etc. 

Many early readers hypothesized that simply enabling Vsync would fix the stutter and runt issues that Frame Rating was bringing to light.  To test this we looked for a game that ran right around the 60 FPS mark in our in normal testing with Vsync disabled and then set about to re-run results with it on.  We are using a standard 60 Hz monitor with the goal of being able to test some 120 Hz capability soon after we figure out a final bug or two with our capture configuration. 

First up, let’s take a look at the NVIDIA GeForce GTX 680 and GTX 680 SLI and see what shows up.

View Full Size

Because the average frame rate per second graph averages out the frame times for a total of one second of time, the averages won’t quite be the straight lines you might have expected.  Looking at the GTX 680 SLI Vsync enabled results the only key item is that the frame rate doesn’t go above 60 FPS like it does with Vsync disabled.

View Full Size

The single card and SLI configurations without Vsync disabled look just like they did on previous pages but the graph for GTX 680 SLI with Vsync on is very different.  Frame times are only switching back and forth between 16 ms and 33 ms, 60 and 30 instantaneous FPS due to the restrictions of Vsync.  What might not be obvious at first is that the constant shifting back and forth between these two rates (two refresh cycles with one frame, one refresh cycle with one frame) can actually cause more stuttering and animation inconsistencies than would otherwise appear.

View Full Size

Based on our graph here we found that with Vsync enabled we had about 87% of our frames running at 60 FPS (16 ms) and 13% at 30 FPS (33 ms).  You might be curious how there could be 60 FPS frame rate so often with Vsync on but very few frames at 60 FPS with Vsync off, and the answer lies in the rate limiting caused by Vsync.  Because of the back pressure on the game engine caused by the longer frame times (30 FPS, 33 ms) from Vsync there is more time for the GPUs to “catch up” and render another frame at 16 ms. 

View Full Size

Our ISU graph on stutter potential tells the story in a more damning light; starting at the 30th percentile the Vsync enabled setup of GTX 680s in SLI are already running at much higher frame variances and it only gets worse as we hit the 60s, 80s and 90s.  At the 90th percentile we are seeing frame variances over 12 ms, which is nearly a complete monitor refresh cycle!

 

Now let’s see how the AMD Radeon HD 7970 results change.

View Full Size

Something interesting is already happening here – the Vsync enabled results from the HD 7970 CrossFire configuration are running at HIGHER average frame rates per second than with Vsync disabled!  The orange line clearly never hits the 60 FPS mark while the black line (Vsync) does. 

View Full Size

Without Vsync we clearly see the runts affecting the plot of frame times here on the HD 7970s in CrossFire but enabling Vsync does appear to eliminate them! 

View Full Size

With our observed frame rate we have the same results for the HD 7970 CrossFire as we did with our FRAPS results, indicating no dropped frames or runt frames.  Standard CrossFire mode still shows the horrible results we have come to expect from our analysis today.

View Full Size

Our Min FPS percentile graph shows us that we are running at 60 FPS (16 ms) 85% of the time and 30 FPS (33 ms) the rest.  Because our data here is based the observed frame rates and not the FRAPS frame rates, there is no correlation between the two CrossFire runs.

View Full Size

The ISU graph of stutter potential again indicates that the Vsync enabled option is introducing higher frame variances than we would like and it is doing it more dramatically and earlier than the GTX 680s in SLI. 

It does appear that enabling Vsync will help alleviate the runts issue seen with AMD Radeon cards in CrossFire but at the cost of much more frame variance and stuttered animation on games that previously didn’t exhibit that problem. 

Let's take a look at another example using CrossFire that has another particular set of circumstances.  I theorized that in a gaming scenario that bordered just under 60 FPS with a single GPU, we would still see problematic results when jumping to HD 7970s in CrossFire.  Take our Battlefield 3 2560x1440 testing: with only one HD 7970 we are running just under 60 FPS most of the time which would, with Vsync enabled, force the game to run at 30 FPS with 33ms frame times.  Ideally we would like to see that move from 33ms frame times to 16ms frame times when adding in another HD 7970 in CrossFire due to the extra performance pushing the card over 60 FPS steady.

View Full Size

Our FRAPS graphs looks how we would hope and expect real-world performance to look.  While the single HD 7970 ran at a non-standard frame rate when performance was under 60 FPS, towards the end (50 sec point) where it could, we see a flat line that is partially hidden behind the pink line.  That pink line represents CrossFire HD 7970s and by doubling the number of GPUs we expected to maximize performance at 60 Hz with Vsync enabled, and we have. 

View Full Size

Observed frame rates calculated by removing runts are showing the Vsync DISABLED results on the HD 7970s in CrossFire mirror what we have seen before with much lower performance.  However, the Vsync ENABLED results did not change! 

View Full Size

The somewhat complicated plot diagram of frame times indicates that at no time did the frame rate of the HD 7970 cards in CrossFire go below 60 FPS or above the 16ms mark - even though there are thousands of frames under 16ms (runts) when Vsync is disabled.  Not only that but performance over the single HD 7970 with Vsync enabled is improved - rather than having jumps between the 16ms and 33ms frame times, we are locked in at 16ms - matching the 60 Hz refresh of our panel. 

View Full Size

The minimum FPS percentile graphic shows the same story - the pink link representing the HD 7970s with Vsync turned on looks solid.

View Full Size

Notice as well that with a static 16ms frame time we see no frame time variance at all in our ISU graph indicating that the kinds of stutter we are searching for are not showing up at all.

How is this happening?  How is enabling Vsync 'fixing' the runts and frame time issues of CrossFire?  The secret lies in the inherent back pressure of vertical sync to pace the graphics card and AMD's CrossFire engines even against its own will.  By forcing the GPUs to only render one frame every 16ms (at the maximum), Vsync is able to force the GPU to pace itself in a way that it would otherwise not.  This doesn't happen in every game though as we saw in the Crysis results first, and there is a lot more testing that needs to be done with Vsync to make a firm decision.

 

NVIDIA has a couple of different solutions in the NVIDIA Control Panel that might help: Adaptive Vsync and Smooth Vsync.  Adaptive Vsync was released with the first Kepler GPUs last year and we found it to be very effective at reducing stutter while also eliminating tearing.  Smooth Vsync is a little known feature that only exists in the driver when SLI is enabled as it takes advantage of many of the same frame metering features that SLI uses.  It attempts to keep frame rates “settled” at a level until it decides it has enough horsepower to move up to the next frame rate option for an extended period of time.  It is a very dubious description at best and NVIDIA didn’t go into much detail on how they decide if they have enough GPU overhead remaining or how long that “period of time” really is.

View Full Size

I decided to run through the same Crysis 3 sequences at 1920x1080 on the GTX 680s in SLI with all four NVIDIA options enabled: Vsync off, Vsync on, Adaptive Vsync and Smooth Vsync. 

View Full Size

Our FRAPS based results show the same similar looking results for standard Vsync on and off, but the adaptive and smooth Vsync options appear to be fixed at 30 FPS with the occasional hiccup on the Smooth Vsync.

View Full Size

The plot of frame times is kind of confusing but the important data is to compare standard Vsync On to Adaptive and Smooth.  With the exception of the 6 or so spikes on the smooth configuration the frames are basically fixed at 33 ms, resulting in a perfectly smooth gameplay experience but at the expensive of limiting performance. 

View Full Size

The observed FPS doesn’t change at all.

View Full Size

Another view here shows the same thing with a fixed frame rate of 30 FPS for adaptive and smooth Vsync options.

View Full Size

NVIDIA’s Adaptive Vsync shows basically 0 variance and only very minimal variance on the Smooth Vsync option at the 96th percentile.  So even though performance is lower on average, the experience is smoother.

 

NVIDIA’s additional Vsync options are definitely a strong point in favor of its technology though the Smooth Vsync only exists on SLI configurations.  I have been told that they were considering adding it to single graphics card configurations and I certainly hope they do as it adds some significant value in the same way Adaptive Vsync and Frame Rate Limiting do.

For both NVIDIA and AMD multi-GPU solutions with standard Vsync, enabling it definitely changes the story.  NVIDIA’s cards pretty much perform as we expected but for CrossFire we didn’t really know what expect with the various visual concerns.  It does appear that the runts problem was at least mostly solved with the enabling of Vsync though to be clear we are only testing a couple of game at this point – much more needs to be done. 

However, enabling Vsync creates a whole host of other potential issues that gamers have to deal with.  Even though the goal of removing visual tearing is met with the option turned on, you do add latency to the gameplay experience, as much as 60ms in some cases, from input to display.  Putting back pressure on the GPU pipeline, for both NVIDIA and AMD, means that some frames are going to be running behind schedule or behind the input timing of the game itself.  Many gamers won't want to deal with those kind of input problems and that is why many still play games with Vsync disabled.  Turning on Vsync does help AMD's CrossFire performance but it isn't the final answer just yet.

April 9, 2013 | 11:18 AM - Posted by Anonymous (not verified)

Thanks Dan,

As you mentioned, there is certainly something to this stuttering. It is worthwhile to continue to optimize the test criteria so that it completely removes any Nvidia bias.

Ryan, can you comment about the possibility of raising the size of the scan lines for runts?

Thanks!

April 9, 2013 | 05:52 AM - Posted by Danieldp

Sorry, double post. XD

April 11, 2013 | 06:46 AM - Posted by Cookie (not verified)

Dan,

Just because Toms hardware is longer around does not mean that they do a better job. My vote goes to Pcper, I prefer to read something proper, no offence to Toms hardware.

April 11, 2013 | 11:53 PM - Posted by Danieldp

Hi,

Not really the point I was making, obviously both sites have sufficient expertise. The thing I was pointing at is the vastly different results...

Dan

April 11, 2013 | 08:22 PM - Posted by Dominic (not verified)

Can you do a test with an APU like the A10-5800K in crossfire with like an HD 6670 to see if this frame rate discrepancy occurs in this circumstance as well?

I would assume it would based on your results but nonetheless I'm curious on its results.

April 13, 2013 | 03:34 AM - Posted by JCCIII

Dear Mr. Stroud and friends,

Thank you for a tremendous amount of work, diligence, and integrity...

I thoroughly enjoyed the video with you and Tom Petersem. Although, I have to mention; I have been very disappointed in Nvidia since my purchase of a group of GTX 480s, believing, from day one, I had thrown away more than $1500 for three unmanageable 1500 Watt hairdryers marketed as graphics cards, which were subsequently relabeled GTX 580s, once the bugs were worked out, kind of like Microsoft's Vista to XP, kind of like scamming on people--no, definitely scamming.

I have always been an enthusiast of the Nvidia since the days of 3dfx and had likewise always enjoyed anticipating and buying Nvidia's new products, and the GTX Titan is awesome.

With memories of ATI, Matrox, and Nvidia (I still have my RIVA 128), a home has been found within my memories, and that is why I am excited about what you and the rest of PC Perspective have done and are going to do. With collaboration you-all are moving a beloved industry onward toward a better future for us and for the companies we want to succeed.

Sincerely,
Joseph C. Carbone III; 13 April 2013

April 18, 2013 | 04:57 AM - Posted by Anonymous (not verified)

All you have to do is use RadeonPro and it will fix all these issues...

April 18, 2013 | 11:29 PM - Posted by CoderX71 (not verified)

This

April 22, 2013 | 09:07 PM - Posted by Anonymous (not verified)

I dont see this huge problem i guess i am blind or only run 1 screen but i have played all titles listed and got better FPS in all of them using my GTX680's and My 7970's.

I still prefer my AMD cards for now for these reason:

1)In benchmarks my AMD cards kill my 680's in crossfire overclocked.

2)Graphics just look allot nicer on the AMD cards.

3)Biggest problem is Nvidia cards Cant Mine!!! (That's the big killer there for me)as id rather make $500.00 off my cards a week if i feel like it and be able to game as well.

I am not an Nvidia or AMD Fanboy as i have 680's in one of my builds and 7970's in a couple others plus have bought many of both cards in between.

I think maybe there is a problem for those running triple screens that hopefully AMD fixes as you have to admit they did a hell of allot on drivers recently that gave huge performance boosts.But 1920 x 1080 60 hertz i have no issues and def a big difference when i add a 2nd 7970 as i have swapped a card to other builds and put it back in do to loss of performance. The other thing i use my cards for is overclocking and Benchmarking and they def show huge performance there.I had my 680's over 1300mhz and they couldn't come close to 2 7970's at only 1225mhz.

So id have to say for working computers i will run my 7970's until there is no more money to be made and i will game on the 680's.

Pretty much not many games need more then 1 card anyway unless running multiple screens and high resolutions, Hell an APU can Max most console port games on the Market but the very few true PC games we actually have.

Yes i agree AMD fix the damn problem. But i also don't think Nvidia fan boys should be rooting for this because if they do the 7970 will be a nasty card all around that's capable of allot more then playing just games.

Just my opinion and experience on the to many cards i have owned to count in my life from both brands.

Take Care

May 5, 2013 | 12:13 AM - Posted by Evo (not verified)

If only we had a tool such as radeon pro to tweak the crossfire to make it operate properly. If only it existed...

The crysis 3 results are a bit questionable as in game vsync was causing havoc for nvidia (input lag) and amd (stuttering). Also crossfire was not engaging properly unless you alt-tabbed (this still occurs half the time). Not to mention the weird fix of opening an instance of google chrome to fix some of the problems with frame rate people were having with AMD setups.

My 7970 cf with radeon pro and other fixes works perfectly for me with Crysis 3, but there are some people still having issues. Also depends when the testing was done as when patch 1.3 was first released it caused massive problems for AMD cards that were later fixed.

May 20, 2013 | 02:17 AM - Posted by tigerclaws12894

Might have a typo or grammar error in the paragraph before the last in the Vsync topic. Anywho, have you ever considered triple buffering on AMD solutions as well as that config on 60Hz vs 120Hz as well? Input latency sure will be an issue but it'd be nice to know if it's better with 120Hz monitors.

May 20, 2013 | 07:11 PM - Posted by ServerStation668 (not verified)

This Dell T5600 has good video benchmarks: https://www.youtube.com/watch?v=3uK1J3o1fks

August 13, 2013 | 09:04 PM - Posted by Anonymous (not verified)

I have read this article four or five times and I find it intriguing. I must admit to not understanding most of it though. However, I must say being the owner of THREE 7970's, MSI Lightning BE, MSI Ghz OC Edition & Club3D RoyalAce at a cost of around £1300.00 GBP, just shy of $2000.00 USD I feel somewhat cheated. I hope AMD's forthcoming "Fixes" will redress these issues. Brilliant article and I am looking forward to all the follow ups.

September 1, 2013 | 02:35 AM - Posted by BryanFRitt (not verified)

What would a game look like if

it got a smooth 120+ fps,
was on a 60Hz display,
and in addition to the regular 'vsync' spot, it would 'vsync' at the '1/2' way spot?
aka update the display at the top and middle, updating at these same two spots every time, and only updating at these two spots.

Would the middle 'vsync' spot be annoying? helpful? noticed? informative? etc...? (This sounds like a good way to see how important fps is)

What's a good name for this?
1/2 x vsync, 2 x vsync, vsync 1/2 x, vsync 2 x, or something else?
What's the logic behind your pick(s)?

September 2, 2013 | 04:39 PM - Posted by lyo (not verified)

(forward note: i have bad english.)
1) is there a diff in observer fps between cards with more ram?
i.e. sli of 2x gtx770 2g vs sli of 2x gtx770 4g?

2) can you publish a min/max/var of partial frame per frame?
insted of runt i wanna know how many different "color" are per frame, and if they are evenly spread.

January 30, 2014 | 12:03 PM - Posted by BBMan (not verified)

Nice review. I'm interested as to how this tech is evolving.
But now I'm curious- I've read some of your test methods- but I may have missed something. I've seen mostly games that are more single player/first-person. Is that part of your methodology? I'm thinking of more intensive object rendering titles like Rome Total War II that has to render myriads of objects and stress memory more. Have you considered something like that?

Post new comment

The content of this field is kept private and will not be shown publicly.
  • Lines and paragraphs break automatically.
  • Allowed HTML tags: <a> <em> <strong> <cite> <code> <ul> <ol> <li> <dl> <dt> <dd> <blockquote><p><br>
  • Web page addresses and e-mail addresses turn into links automatically.

More information about formatting options

By submitting this form, you accept the Mollom privacy policy.