2 lesser GPUs vs 1 better?

[Charlie98]

This has probably been axed before, but I'm not getting anything back on search...

I understand the basic purpose of SLI/CrossFire with 2 GPUs and was wondering...

Would 2 lesser cards SLI'ed be 'better' than one better card? For example, 2 550ti's SLI'ed vs 1 560ti. The core count winds up being the same, but does the dual setup pick up any efficiencies over a single card with the same amount of cores? Or more cards split between 2 PCIe slots would just slow everything down...?

Cost-wise, 2 cards would be just a little more expensive, but if there is some benefit over the single card it might make it worth it.

 

[MrK6]

It's generally the other way around. Two GPU's usually have more setbacks than a single card, and therefore it's generally recommended to stick with the fastest single GPU card you can get (unless there's nothing faster and then you're forced to go CF/SLI, but I don't think that's where your inquiry's focus is). As you can imagine, syncing two GPU's to run together is a lot more complicated than getting one GPU to do the same rendering. Because of this, drivers play a big role in the kind of playability and performance (or lack thereof) that you will get. Also, generally speaking, a multi-GPU configuration of similar "raw" performance as a single GPU configuration will have higher maximums and lower minimums. There's also the phenomenon of microstuttering, which is a byproduct of the Alternate Frame Rendering currently employed by multi-GPU technologies. Basically, your reported framerate per second will feel slower/glitchier/jerkier in a multi-GPU configuration because the actual framerate, especially when looking at frametimes, is slower. Then there's the other drawbacks of running two GPU's/cards, generally being more noise, more heat, etc.

 

[Charlie98]

There's also the phenomenon of microstuttering, which is a byproduct of the Alternate Frame Rendering currently employed by multi-GPU technologies.

I didn't know that... very interesting.

 

[boxleitnerb]

If you get a good deal, though and care rather for image quality than high fps, SLI/CF with two lesser cards might make sense. Microstuttering can be a thing of the past if you employ a frame limiter. Eats up some of the scaling, of course, but you will most likely be able to use settings that you couldn't with one GPU.
See my thread here about this:
http://forums.anandtech.com/showthread.php?t=2218236

 

[Red Storm]

I prefer to buy one self-deprecating card rather than two, especially since I almost always sell my current card to upgrade.

And console ports have done a fantastic job of making high end cards (let alone two) quite unnecessary.

 

[dust]

2 better GPU's.

/thread

 

[Tempered81]

I'd rather have a single over two.

If it's a big difference i'd take the two. two 570s > 1 580, two 4870s > 1 4890.

In most cases I'd prefer 1. two 5870s < 1 7970. two 460s < 1 480.

 

[BD231]

If you enjoy pumping out 150+ FPS in any title you can imagine you go with a dual config, if you're lame and somehow can't manage to get SLI/CrossFire to work to your liking you go with a single high end card and end up paying 1/3 to almost double more for less performance than you'd get out of a dual config with 2 lesser cards. For instance 2 460s are just as fast as a GTX 580, but in most cases faster. All a matter of shader count of course. GTX 580 has 512, two gtx 460s have almost seven hundred identical cores. Dual 560ti's get you well over 700 and at that point the 580 can't compete.

The only issue is frame buffer (which at 1gb isn't an issue for 99% of the games available), but even with the 580 you're still limited to 1.5mbs which for a game like BF3 isn't enough in itself. People really do bitch and complain about SLI/CrossFire problems but for the life of me I can't reproduce the issues people complain about on these forums, the sh t just works. Micro-stutter issue is a joke, any popular games have ample compensation through game profiles and you can't compare the smoothness of 150+ fps to a single card, it's a completely different experience.

 

[boxleitnerb]

What do you mean by "microstutter issue is a joke"? Do you mean to say it is a non-issue?

 

[BD231]

What do you mean by "microstutter issue is a joke"? Do you mean to say it is a non-issue?

Pretty much. The only issue I run into is my GPU's throwing *WAY* to many frames at my CPU because a game engine is already running at 100+ fps with one card, in which case I just disable dual gpu for that game instead of watching the ensuing slide show. But yeah for the majority of quality titles microstutter is not an issue. I've heard some people say some are more sensitive to it, but when you're pushing over 100fps it gets awful hard to notice, especially with a good game profile and engine. One thing people fail to mention is that it doesn't mess with the fluidity of a game, so while you might notice a frame overlap once in a blue moon it's not a deal breaker like taking a dive to 20 fps with a single card would be.

 

[boxleitnerb]

Sure, even above 60 I don't notice it. But I don't need SLI/CF for 100+ fps (I play with Vsync anyway). I rather enable eyecandy and then I'm at 30-60 depending on the game. I depends on how you play.

 

[nanaki333]

i used to be all about the better single GPU.... but then they started doing the dual GPU on a single card... i started buying the dual GPU cards and realized the pros outweighed the cons, and then bought my first real crossfire 6970 setup (upgraded from 5970).

 

[BD231]

Sure, even above 60 I don't notice it. But I don't need SLI/CF for 100+ fps (I play with Vsync anyway). I rather enable eyecandy and then I'm at 30-60 depending on the game. I depends on how you play.

Another good point, if you Sli/CrossFire and don't mind using V-Sync that's about the best reported solution available for micro stutter. You can effectively eliminate it with that feature, should you ever need to.

I hear you on eye candy though I like to crank everything up to max myself, but there's only one game I play so far that limits me on eye candy which is BF3. If I turn down shadows/special effects a bit and leave everything else at ultra its a non issue and still looks great though. Definitely going for 2gb cards the next time I purchase, its a shame good hardware can be so easily limited by something as cheap as memory. If any of the Kelper leaks are valid we're going to see a flood of 2gb options in the value sector, which is really what needs to happen considering some of the games that are coming out lately.

 

[boxleitnerb]

Vsync doesn't really help with microstutter. Maybe a tiny bit, but for instance 35fps with and without vsync will both stutter bad.
I mostly play with SGSSAA so I'm quite often in that situation.

 

[BD231]

Vsync doesn't really help with microstutter

 

[boxleitnerb]

All the tests in my link were conducted with vsync on. I only play with vsync and without a frame limiter I always notice microstutter if fps fall below 40-50 depending on the game.

 

[MrK6]

As you can see OP, there people (and a good number of them) who buy into the marketing and only look at the FPS encounter. However, I understand it's difficult to know how uninformed you are if you've never experienced the alternative. NVIDIA knows it can't sell a GTX 580 to everyone, but if they can get them to buy two GTX 560 Ti's (or GTX 460's), that's still pretty decent in their bottom line. Same goes for AMD, and that's why you'll see neither company mention the drawbacks of multi-GPU as they're trying to sell as many cards as they can. If you want to get educated on the subject, here's a great article that highlights a lot of the issues: http://techreport.com/articles.x/21516/11

 

[Charlie98]

However, I understand it's difficult to know how uninformed you are if you've never experienced the alternative.

I'm literally a babe in the woods as far as modern computing goes, GPU's specifically... that's why there is still the awful void in my build where that GPU needs to be. I'm coming from a 6-year old Dell, and I'm still using the Intel graphics on my 2500K... so, no, I'll admit ignorance.

Aside from the OC board, I've seen more sharply divided posts here in video than anywhere else (or so it seems.) Sometimes it's like the gunfight at the GPU Corral.

This is all very good information and gives me something to think about and research.

 

[MrK6]

I'm literally a babe in the woods as far as modern computing goes, GPU's specifically... that's why there is still the awful void in my build where that GPU needs to be. I'm coming from a 6-year old Dell, and I'm still using the Intel graphics on my 2500K... so, no, I'll admit ignorance.

Aside from the OC board, I've seen more sharply divided posts here in video than anywhere else (or so it seems.) Sometimes it's like the gunfight at the GPU Corral.

This is all very good information and gives me something to think about and research.

Excellent, and congrats on your new build. In the end, we're all just sharing opinions (even opinions on the facts), and what may bother one is undetectable by another. I think it's wise to do as much research as you can, get a look at the whole picture, and then develop an informed opinion. Best of luck in your endeavor :thumbsup:.

 

[Quantos]

As you can see OP, there people (and a good number of them) who buy into the marketing and only look at the FPS encounter. However, I understand it's difficult to know how uninformed you are if you've never experienced the alternative. NVIDIA knows it can't sell a GTX 580 to everyone, but if they can get them to buy two GTX 560 Ti's (or GTX 460's), that's still pretty decent in their bottom line. Same goes for AMD, and that's why you'll see neither company mention the drawbacks of multi-GPU as they're trying to sell as many cards as they can. If you want to get educated on the subject, here's a great article that highlights a lot of the issues: http://techreport.com/articles.x/21516/11

Very good article. I just read that (I'm totally not at work). That only reinforces my skepticism of dual-GPU setups.

 

[BD231]

http://www.overclockers.com/micro-stutter-the-dark-secret-of-sli-and-crossfire

Forums everywhere seem to be full of everything from micro stutter horror stories to flat out denials of its very existence

*NEVER* had a single instance of micro-stutter the way it's described by some folks that tuck their tails and run. Why? Because I'm not floating around 30 FPS where it clearly starts to become a problem.

 

[Quantos]

Well if Nvidia and AMD's engineers both not only say it exists, but that today's card already have systems to counter it (partially), I'd say denying its existence is a bit stupid.

 

[exar333]

I myself prefer a single good GPU over 2 'OK' GPUs. 2 good GPUs (or better) are really needed for very high res displays. That said, sometimes a little less GPU power, but more memory, can help more in high resolutions. 1 single GPU with 3GB memory could be better in some situations than 2 GPUs equaling 110% of that performance, but with only 1GB.

 

[MrK6]

http://www.overclockers.com/micro-stutter-the-dark-secret-of-sli-and-crossfire

Forums everywhere seem to be full of everything from micro stutter horror stories to flat out denials of its very existence

*NEVER* had a single instance of micro-stutter the way it's described by some folks that tuck their tails and run. Why? Because I'm not floating around 30 FPS where it clearly starts to become a problem.

If you have to keep your frametimes high above your monitor's refresh rate so that you don't notice microstutter, that defeats the purpose of going dual GPU, doesn't it?

Like I said, people get sucked into the marketing and only look at the FPS counter, which doesn't tell the whole story. Because of microstutter, you're only getting a small fraction of return on the huge investment of a second card. It's very simple to understand this concept if you look at individual frame times. Let's say you have a single GPU capable of running a game at 30FPS. Let's say it also has great drivers with perfect scaling (lol) and you can add in a second GPU to get 100% more performance. The FPS counter will say 60FPS, but the frametimes will tell a different story. At 30FPS, each from is rendered on average every 33.3ms. Note that even on a single GPU, there will be irregularities as the scene changes, but they are very small deviations. With the two GPU's at 60FPS, you'll see an average frame time of 16.7ms, but the actual frame times vary much more greatly. Generally there's a sort of stacatto type patter where an odd frame is rendered followed closely by the even frame, then a longer period before repeating. So within the average frame time of 33.3ms for two frames (2x 16.7ms), frame 2 is rendered after frame 1 in 10ms, then there's a 23.3ms wait. That wait gives us the phenomenon of microstuttering, so now you're actually only getting 1000/23.3ms = 42.9 FPS.

Therefore, even though a benchmark or an FPS counter will tell you you're getting 60FPS and double the performance, the game plays and feels no differently than if you were playing on a single GPU at ~43FPS. That's why multi-GPU is a poor return on investment and should only be entertained when there are no other options left on the table to increase performance.

Now I should also add that you can minimize microstuttering by adding more GPU's into a multi-GPU array. Even Tri-Fire or Tri-SLI will do a lot to break up that "lag" period scene in dual-GPU configurations. But, that adds more driver problems, scaling issues, and overhead, in addition to cost, noise, heat, etc. There's a great video out there using HL2 and a high speed camera that show that "stacatto" rendering due to microstutter, but for the life of me I can't find it atm.

 

[BD231]

Well if Nvidia and AMD's engineers both not only say it exists, but that today's card already have systems to counter it (partially), I'd say denying its existence is a bit stupid.

I understand it's difficult to know how uninformed you are if you've never experienced it.