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PCIe bandwidth usage?

G

Ghozur

n00b
Joined
Oct 26, 2014
Messages
37
Hey all! So for the first time I'll be running 2 GPU's and find myself wondering if my current setup will make the cut.

So I'm planning my system for the game Star Citizen. According to the Devs it's going to be pretty heavy physics wise. And it's going to be a PhysX enabled game. So my setup will be one current gen (at the time) high end card to run an Oculus Rift and a second card being a previous gen high end card to run PhysX.

My current setup is an i5-3570k so I'm not worried about CPU power, but with the limit at 8x lanes for 2 cards I'm wondering about PCIe bandwidth. I haven't been able to find anything about how much bandwidth is used by PhysX and I do know that higher FPS (which you kind of need for the Rift, it would seem 75-90fps) uses more bandwidth.

Now I have done a bit of Google searching and found an article at Tech PowerUp that shows scaling with a 680 that shows that x8 is fine and x4 shows only a 2% performance loss. And a article at Anand Tech with 2 Titans in SLI that shows up to a 7% boost going from x16/x16 PCIe 2.0 to 3.0. Which is a very different result from the TPU article.

So my options seem to be:
1) Upgrade to PCIe 3.0 x16/x16
2) Wait for PCIe 4.0 and do a new x8/x8
3) Wait for PCIe 4.0 and do x16/x16

I'm leaning to 2 or 3 since the game won't be out until likely late next year so that will be right around SkyLake. Any thoughts from my fellow enthusiasts?
 
Generally speaking PCIe 2.0 SLI 8x/8x is not going to hold you back much. A few FPS, which would instantly be negated by the drastic increase you get from SLI.

Nobody is really taking the PCIe numbers seriously anymore because tests already have confirmed that it is no longer a limiting factor since 2.0. You'll be perfectly fine with 2.0 and two video cards in 8x until you upgrade years down the road and the motherboard happens to have PCIe 3.0/4.0 or 8.0. Game Devs take into consideration they will NOT send any data across PCIe lanes unless they absolutely have to because latency, THEN bandwidth is so bad compared to on the graphics board.

tl;dr
You're fine. Don't stress yourself. PCIe is hardly a limitation anymore. If you want to blow money on a senseless upgrade for a new MOBO I wont hold you back.
 
I've actually been wondering the same thing with regards to micro stutter. Average FPS is one thing, but I'd love to see frame time charts and cannot find them. The closest was a 5820k vs 5830k was 5% slower with 28 vs. 40 lanes. (8x vs 16x). I wonder if the frame time variance is 5% or much greater.
 
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Rav3n thanks! I was surprised I didn't see any follow ups to the extensive testing they had previously done. But I guess I just wasn't looking in the right places.

Overall it looks good, but in the games that use the Cryengine 3 like Star Citizen it looks like it's making a difference. Nothing huge for sure.

durquavian good point, but my next upgrade would be late 2016 (I tend to upgrade the CPU/MoBo every 4 years) so with SkyLake unlocked chips likely to be early 2016 that's close enough to put some serious thought into.

Dayaks are you looking at the Rift as well or just interested in micro stutter for other reasons?
 
Dayaks said:
Very curious how different processors / PCI lanes correlate to microstutter.
Click to expand...

They won't. Microstutter is an issue with the frames not being sent out at even intervals.
As long as you have a sufficient amount of PCI-e lanes for your cards the difference in frametime will not be affected enough to get results outside the MOE.
 
Ghozur, nothing specifically just stutter in general.

LordEC911, but I am just curious why they are not being sent out at even intervals. PCIe lanes can be irrelevant as long as you have 8x PCIe 3.0's, ect. and if I had to guess I'd agree with you. What causes most frames to be at say, 16 ms then it jumps to 50. CPU, GPU, PCIe lanes, PLX controllers, software, ect?

In this thread (linked) the only reason anyone attempted to give was that the CPU wasn't feeding the 970 SLIs fast enough and the frame times went bonkers. http://hardforum.com/showthread.php?t=1846926 I'd assume it's a bottleneck at the CPU itself, and not the bandwidth between the CPU & GPU, but I would love real data which it looks like techpowerup may generate for us.
 
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Ghozur said:
durquavian good point, but my next upgrade would be late 2016 (I tend to upgrade the CPU/MoBo every 4 years) so with SkyLake unlocked chips likely to be early 2016 that's close enough to put some serious thought into.
Click to expand...

It's possible that we'll have PCI-E 4.0 products in 2016 (though not definite), so hopefully you can buy that for your upgrade by that time.
 
dandragonrage said:
It's possible that we'll have PCI-E 4.0 products in 2016 (though not definite), so hopefully you can buy that for your upgrade by that time.
Click to expand...

That's my plan. If it doesn't release with SkyLake I very well may wait until it does since I don't think I'm currently hurting for CPU power for gaming.

The Intel slides currently show PCIe 4.0 with SkyLake-E. Don't usually go for an E chip, but my finances are better than they have been in the past so I may go for it lol
 
If don't mind me tagging along in this thread as I have a similar question specifically also for Star Citizen (and maybe other Physics games also).

If I went SLI 980's (or something along 980ti/whatever nvidia releases this summer/fall) ,

1. Would a 750ti dedicated physics card help with min frame rates in games that used PhysX , especially if running 4k.

2. What platform do you need to go with to stay at least 8x on both SLI main cards ? Would it require the X99 chipset or is there a Z97 that can get you enough on the PCIE lanes for 2 980's and room for 750ti dedicated PhysX?
 
1. http://hardforum.com/showthread.php?t=1843871
And there are older reviews floating around the web.

2. A Z97 should be able to keep at least 8x. I know the higher end Asus use PLX chips to do it. My next rig (likely Skylake) I am going to go X99 though especially if I am going high end SLI.
 
I wouldn't count on it that Star Citizen ever makes heavy usage of PhysX because at the moment they do not even use it nor support it.
 
Tup3x said:
I wouldn't count on it that Star Citizen ever makes heavy usage of PhysX because at the moment they do not even use it nor support it.
Click to expand...

I imagine they will from their track record so far. They seem to be taking their time to do it right. OP might just be onto his next build by the time it happens. :)

To Tup3x's point you could always wait until it is implemented and to what level, then buy a Physx card if it makes sense. By then the cards might be dirty cheap.
 
Dahkoht - Not at all, PhysX is extremely relevant. Everything I've seen shows FPS benefits to having a dedicated PhysX card for games that use it. How much seems to depend on how much PhysX features the game uses.

Tup3x - As Dayaks said, the Devs mean business. So far their track record with doing things right is good. If they say their going to do it, I'm rather confident that their going to do it. With the game being crowd funded, the only people they have to please are the end users who want it done right not the publisher who wants it done yesterday.

Dayaks - I actually am trying to time the build to just around the release of the game. First time I've done it too, but this game is pretty much my dream game. I was a Wing Commander addict as a kid and then got into multiplayer. Both of those things with the Occulus Rift??? That's like a dream come true for me! lol
 
Ghozur said:
Dahkoht - Not at all, PhysX is extremely relevant. Everything I've seen shows FPS benefits to having a dedicated PhysX card for games that use it. How much seems to depend on how much PhysX features the game uses.

Tup3x - As Dayaks said, the Devs mean business. So far their track record with doing things right is good. If they say their going to do it, I'm rather confident that their going to do it. With the game being crowd funded, the only people they have to please are the end users who want it done right not the publisher who wants it done yesterday.

Dayaks - I actually am trying to time the build to just around the release of the game. First time I've done it too, but this game is pretty much my dream game. I was a Wing Commander addict as a kid and then got into multiplayer. Both of those things with the Occulus Rift??? That's like a dream come true for me! lol
Click to expand...

I completely agree with you. Honestly I try not to think about SC too much because it is so far out. When I do think about what games I am really looking forward to it's Battlefront, SC and Legacy of the Void. So it's a top three game for me. I do have an Aurora LN package, I let my 6 year old girl pick and she want it... because of the Disney princess. I imagine they can heavily use Physx inside the station battles, ect. If I was a software engineer with "no limits" Physx is a really cool toy to play with.

Now you have me thinking of doing Oculus Rift! I'm thinking my next build will be November 2016 and going all out. Will probably coincide with Star Citizen and my third child beginning to use a computer. Funding it is a bit tricky, I am thinking about buying Newegg gift cards every time my wife goes to the Spa ($130/every two weeks). That should add up! lol.
 
Dayaks said:
I completely agree with you. Honestly I try not to think about SC too much because it is so far out. When I do think about what games I am really looking forward to it's Battlefront, SC and Legacy of the Void. So it's a top three game for me. I do have an Aurora LN package, I let my 6 year old girl pick and she want it... because of the Disney princess. I imagine they can heavily use Physx inside the station battles, ect. If I was a software engineer with "no limits" Physx is a really cool toy to play with.

Now you have me thinking of doing Oculus Rift! I'm thinking my next build will be November 2016 and going all out. Will probably coincide with Star Citizen and my third child beginning to use a computer. Funding it is a bit tricky, I am thinking about buying Newegg gift cards every time my wife goes to the Spa ($130/every two weeks). That should add up! lol.
Click to expand...

To me the Occulus Rift seems amazing for any kind of first person gaming. I've been wondering why it's been so long in a company getting 3d goggles into the consumer space. So about time I say.

$130 every other week??? That's like $3400 a year or something! May want to think about getting yourself another ship for SC while yer at it! lol
 
You need 3.0 if you're doing tri-sli on a 10+ mp setup. When I tried to run 3 titans at 7860*1600 it was not pretty with pcie 2.0. The experience was like playing on a card that did not have enough vram. Switching to a 3.0 setup made the cards perform as they were supposed to.

A dual gpu card like a titan z might also benefit. Otherwise any gain would be marginal on less exotic builds.
 
Game's not gonna be out till like 2016. Worrying about a build right now is just silly. See what's out if/when that 2016 release date materializes.
 
http://www.pcper.com/reviews/Proces...-Processor-Review/Multi-GPU-Gaming-Performanc

Found that at pc perspective. It has frame times for the 5960x vs 4790k. Looks like the extra lanes don't help a whole lot, all processors looked about the same. I wish they used a resolution that at least allowed 60FPS on all games (more processor intensive)... They used 4k. Looked like the 5960x pulled ahead a little on games with higher FPS, insignificant, but better. Also I don't think they were OC'd for that review and the 5960x has a ton of headroom.
 
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