Is Anyone running Crossfire at PCIe 2.0 x16 and x4?

[20mmrain]

It's just like the question up on top..... is there anyone here who is doing that? And if so how bad is it crippling your performance?

I have read the review here at TPU looking at the performance gaps in PCIe Lanes.....but know one has done that same report in related to Crossfire not just single cards.

I have a few questions about it......

1. If you are running Crossfire at those lane speeds ..... when the one cards performance is lowered does the other cards performance lower too?

2. I could find one account about this subject on the net..... that person said his 5850 setup ran worse in Crossfire than it did when he had just one card in is this true?

The reason I ask is because tax returns are coming back. I am trying to decide between buying a 5970 (and just keeping it a single card in my rig) or

A new Mother board and a 5850 along with it to match up to my 5870 that I already have. So I would in turn have a 5870 + 5850 Crossfire setup.

Any comments or thoughts? Thanks

 

[erocker]

I would expect minimal and non-noticable difference with x4 in CrossFire on the 2nd card. Whoever put a 2nd card in their rig and got worse performance had problems that had nothing to do with PCI-E lanes. Nothing wrong in CrossFiring a 5850 + 5870 as long as you don't mind not having the open expansion slots on your motherboard.

 

[MKmods]

personally I just want x16 times 2 no matter what.

But there was a review here that said the dif was not that big (on X8 and x4), now add to that the second card dosent seem to be as forced as the first and I bet the dif is even less.

Honestly is a 5870 not enough?(I would imagine another card with a 20" lcd is a serious waste of GPU)

 

[20mmrain]

I would expect minimal and non-noticable difference with x4 in CrossFire on the 2nd card. Whoever put a 2nd card in their rig and got worse performance had problems that had nothing to do with PCI-E lanes. Nothing wrong in CrossFiring a 5850 + 5870 as long as you don't mind not having the open expansion slots on your motherboard.

Thanks for the quick response...... Yeah I have no problem with Xfireing the 5850 with a 5870 either. The only reason I was maybe thinking of going that way is because of the extra cost of buying a new motherboard if there would have been a huge performance drop in Xfireing a x16 lane and a x4 lane.

But if I get enough answers here confirming the same thing you just said..... I might skip the new board and just get another 5870.




You know how it is though...... it just sucks getting your hopes up when buying something new and then getting it here and finding out you can't use it...... or you have to buy something else to get it to work. Especially when it's 400 bucks.

personally I just want x16 times 2 no matter what.

But there was a review here that said the dif was not that big (on X8 and x4), now add to that the second card dosent seem to be as forced as the first and I bet the dif is even less.

Honestly is a 5870 not enough?(I would imagine another card with a 20" lcd is a serious waste of GPU)

I am playing at a res of 1920x1080p normally and sometimes on a 37 inch T.V. ...... So I could use the extra performance and not be wasting it

I did read the article.... but From what I remember (it was awhile ago) it was just talking about the cards by themselves in the X16/x8/x4 slots and not what the scaling is when they are running Xfire.

So I was really wondering how that would translate into performance. To see if buying a 5970 and selling my 5870 was worth it or would I be better off just buying another 5870 and Xfireing the one I already have.
Or the other option there was ..... buy a new MOB and then a 5850 with it and Xfire it that way.

Maybe I should list my specs to help with the advice.....

Intel i5 750 @ 4.0ghz
EVGA P55 LE
Corsair XMS3 @ 1600Mhz 9-9-9-24
Diamond ATI HD 5870@ 915/1300
2x Western Digital Balck Carvers 500Gig
Corsair 750 TX PSU
CM Sniper Black
Corsair H50
Res: (normally) 1920x1080p (Sometimes) with two added 16 inch monitors @ 1024x768 each (Sometimes) on a 37 inch TV res @ 1360x768

 

[DriedFrogPills]

if you are going to get another p55 board just get one of the boards that splits the x16 link from your cpu into 2 x8 links. that said can't your mobo do x8/x8?

and here is the link for pci-e scaling for ati

http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/

 

[20mmrain]

if you are going to get another p55 board just get one of the boards that splits the x16 link from your cpu into 2 x8 links

Yeah but I f I could get another 5870 with out having to buy a new Motherboard I could spend the extra money on ..... like water cooling or something.

 

[DriedFrogPills]

yeah the x8 link doesn't really hurt the 5870 so if your board does support x8/x8 you will be fine,

ok my bad. looked at the evga website. if you did add in a second card it would be okish as x4 only takes a 5% hit looking at the graphs had me thinking about trifire on my mobo. then the price stopped that thought process.

 

[crazyeyesreaper]

you need to remember x4 PCIe 2.0 is the same as 8x 1.1 so you wont notice the difference

and if your going to crossfire at 1920x1200 its less then 1 FPS difference between x4 and x16 in crysis

 

[20mmrain]

you need to remember x4 PCIe 2.0 is the same as 8x 1.1 so you wont notice the difference

and if your going to crossfire at 1920x1200 its less then 1 FPS difference between x4 and x16 in crysis

Actually that is some great reporting bud!..... Well it looks I am going to go with an extra 5870 and ..... maybe my first real water cooling kit.... either that or an SSD

I will report back when I find out the performance.

 

[crazyeyesreaper]

no problem man i just loaded tpus review lol and reported the info you needed

 

[cadaveca]

Cost vs performance in 16x4, Crossfire isn't worth it.

Tried it...x1900's, x1950's, 2900's, and more...adding the second card didn't add very much performance-wise...makes more sense to sell current card, adn then upgarde to a better single gpu.

FYI, you cannot take single-card pci-e performance numbers, and then relate that to dual-card..doesn't work that way. NO inter-gpu communication over the pci-e bus with a single card. Best-case scenario is 25% performance boost(as most crossfire gives is 150%-170%). You lose and avg 15% going to 4x, and double that loss, and most times greater, due to having little-to-no bandwith left for the cards to communicate on.

So factor in that each card only runs about 75% of it's max, when in crossfire, take 30% off that 75%, and add it to your 75% from the other card. Barely more than 1 card, isn't it?

 

[crazyeyesreaper]

http://www.tomshardware.com/reviews/crossfire-meets-pci-express,1761-4.html

1.0 at x8 x8 is x4 x4 for pcie 2.0 from what i see there he would still get a boost if i could limit my boards pcie lanes id run tests myself with 2 5850s at x8 + x4 just to see but im not sure thats possible

in that test granted its older gpus x8 x8 is the same as x4 x4 and comparing the same gpus on pcie 2.0 x16x16 it was a 12% difference

 

[cadaveca]

Just tape off the lower card's slot...

I tried P35 and P45 last, not P55, but I doubt it'll make much difference, being a different chipset...you get a boost, but it's barely worth it...to the point that I tihnk they should never put a 16x connector on a 4x electrical slot...

I mean, you know what I'm talking about by only getting 150% with two cards if you have two...so it's only logical to expect less than that, no? So paying full price for less than half a boost...just doesn't work. It's all about how much more performance you get for that price.


I admit my perspective isa bit skewed..I've been running 2560x1600 since 2007, and been chasing decent performance at that res sincie then. So I'm definately one to need the best possible, and that's 16x16...

 

[crazyeyesreaper]

well im running a Phenom II x4 940 and in crysis i only use 55% of both gpus as it is do to cpu and memory bottleneck on i7 he would still see higher frame rates then i do period on x8x8 on the 790gx platform simply because the i7 offer better multi gpu scaling in his case selling the 5870 and grabbing 2 5850s to overclock along with a new mobo could be a better idea and sell the other mobo to make up the difference if it matters that much but im still willing to bet he would see a good increase performance wise not as good as x16 xfire but still a sizable increase

true but at x4 at 1920x1200 in crysis theres a 1fps difference and even me at x8 x8 i only see 15 extra frames from crossfire in that game and the performance increase he gets will be noticeable as again x4 2.0 is = to x8 1.1 and most of these gpus still perform just fine at x8 x8 1.1 spec if he was using an older setup ie 1.0 or 1.1 at x4 id agree thats not gonna cut it but x4 on 2.0 i believe will be enough to warrant another card


hell who knows if he gets another card he can test his motherboards abilities with crossfire and we can get a definitive answer

 

[cadaveca]

Yeah, i'm not saying there wouldn't be a boost, but it's just like running 3870x2 Crossfire. At high res, it's gonna choke. The 3870x2's PCI-E 1.1 switch caused the same problem. When a single Crossfire connector is only .9GB/sec, extra frames must travel via PCI-E, making for very limited cpu-gpu communication...almost like making the cards have just 2x, or 3x connection. I'd like to see if I'm right, and as the framerate goes up, it gets worse...

 

[crazyeyesreaper]

yea but again man that 1.1 spec at was half the bandwith he has avaible im willing to think the issue with the 3870x2 was more the fact its 4 gpus sharing 2 slots as 2 regular gpus i think would be half the strain id gamble and go for it if i was in his place as his system even at x16 x4 with 2 cards will rofstomp my x8x8 setup

i wish i had time and proper skills to test this id like to see some good tests run on a crossfire and sli setup to see how it impacts performance

if x16x4 can provide a boost within say 10% of x16x16 id simply buy an x16x4 board depending on the gpus i was using if you get my meaning example the asus 785g board thats x16x4 if that config showed withing 5% of x8x8 and 10% of x16x16 id have no reason to shell out for a $200 mobo when a $90 board gets me the same thing or there about

 

[cadaveca]

They've mentioned that they have changed the way Crossfire works, so I wonder....it's an interesting question, for sure.

I wonder if eyefinity would further complicate things too...

 

[crazyeyesreaper]

good question damn this thread now i have questions i cant find answers to

 

[cadaveca]

You'd think that if mobo makers were smart, 8x8 boards would be wired to have the remaining 8 lanes interconnected external to the chipset, like how we used to have to flip the paddle with the Nforce Sli boards...anyway, it would make 8x8 far better than 16x4...

 

[overclocking101]

ran X16-X4 at first on this setup i have now. Ran fine. increase in performance for sure. not as good as X8-X8 but still better performance than 1 GPU

 

[crazyeyesreaper]

can you do a comparison say a quick and dirty 2-3 games ?