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AMD Radeon HD 5870 PCI-Express Scaling

Mussels

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Guys, one question.

I have an Asus P5Q Deluxe mobo with 1 PCI-E x16 and 2 PCI-E x8. I'm running now an 5770 on the main slot, but I'm thinking to buy another card and Crossfire-it. The question is, are those 2 cards going to run on x8 or only one of them? I'm also curious what's the performance drop between x16/x16, x16/x8 and x8/x8

thanks.

both run on 8x. performance hit will be next to nothing.
 
T

TAViX

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Good to know. I was asking because all the Crossfire review I've read they use mobos with 2xPCI-E x16, so I was kinda reluctant about this...
 

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@w1zzard. I have some doubts with the conclusion of the review.

Some motherboard manufacturers are offering a third PCI-Express x16 slot that is electrically x4. The results show that the performance drop isn't as bad as one would imagine, so we will green-signal installing a third accelerator for some 3-way ATI CrossfireX action, or 2-way CrossfireX on entry-level Intel P55 motherboards with the second x16 slot electrically x4 (running in 1.0 mode). If you're crazy enough to mod a PCI-Express x1 slot (by carefully cutting its end to let it seat a PCI-Express graphics card), then the scores should really dishearten you. Buy one of these accelerators now, add one later, and you will have secured yourself future-proofing.

- Isn't it so that 2 card in xfire need more PCI-e bandwith in comperison to 2 seperate cards? (cards in xfire mode exchange data between each other = more bandwith needed?)
- The reason why the second (or third) PCI-e x16@x4 is PCI-e 1.1 is because these PCI-e lanes are connected to the P55 chipset (and not like the PCI-e x16@x16 (2.0) connected to the CPU). The bandwith between chipset and CPU (DMI) is 2GB/s = equal to PCIe X4 (1.1)



So the bottleneck won't be the X16slot@X4 but the DMI which has to share it's bandwith with SATA, USB, VGA, LAN etc.
 
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Benchmark Scores Faster than yours... I'd bet on it. :)
First, GREAT write up!

I have a question though. Doesnt the use of AA increase bandwidth needs? Be it between the cards or other interfaces? What would this test look like if you put varying AA levels on it?

Thank you in advance for your reply.
 
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Benchmark Scores Faster than yours... I'd bet on it. :)
BUMP... its been days since i posted this...

Anyone... especially the person who wrote this article.......HELLO??
 

Mussels

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w1zzard is a busy fellow.

Even if he wanted to test this, it'd probably take him a few days to get the test system set up for it again.


Roberto72: you're forgetting the crossfire/SLI bridges between the cards, most of the data goes across there directly.
 
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First, GREAT write up!

I have a question though. Doesnt the use of AA increase bandwidth needs? Be it between the cards or other interfaces? What would this test look like if you put varying AA levels on it?

Thank you in advance for your reply.

I can reply.


First, use google.

Second, AA only uses more PCIe bandwidth if it has to offload texture data to main system meory to make more room for the AA cache, if you are doing that then you have other problems. With how fast the new vmem is, and the bandwidth available to the GPU die, and the implementation of the stream process for handling AA and other filters, the effect on performance is minimal.


C) AA is less of a issue at larger resolutions, implementing multiple types of AA on objects in a scene to remove that 1 pixel wide jaggie does nothing. So burn your bandwidth on something useful, like a game worth enjoying.
 

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Roberto72: you're forgetting the crossfire/SLI bridges between the cards, most of the data goes across there directly.

CFX bridges pass 0.9 GB/s of data.
 
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Benchmark Scores Faster than yours... I'd bet on it. :)
I can reply.


First, use google.

Second, AA only uses more PCIe bandwidth if it has to offload texture data to main system meory to make more room for the AA cache, if you are doing that then you have other problems. With how fast the new vmem is, and the bandwidth available to the GPU die, and the implementation of the stream process for handling AA and other filters, the effect on performance is minimal.


C) AA is less of a issue at larger resolutions, implementing multiple types of AA on objects in a scene to remove that 1 pixel wide jaggie does nothing. So burn your bandwidth on something useful, like a game worth enjoying.
Thanks for that utterly BRILLIANT suggestion to use google genius. I did try, however my search turned up nothing that directly answered my question. For pete's sake its not like I asked "how to overclock" and had the answered plastered all over 2342423 stickies at 23423542 sites...

Aside from that, I sincerely appreciate the response. ;)

w1zzard is a busy fellow.

Even if he wanted to test this, it'd probably take him a few days to get the test system set up for it again.


Roberto72: you're forgetting the crossfire/SLI bridges between the cards, most of the data goes across there directly.
Yeah I wasnt looking for re testing or anything. A reply like Speedo (minus the BS "google" reply) was what I was looking for. Thanks!!! :D
 
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SummerDays

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BTA, can you please provide a reference for the 0.9GB/s on the crossfire link? Thank You :)
 

cadaveca

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Top orange link is Crossfire interconnect(CFBI), listed @ 0.9 GB/s....slide shows one shared between the cards on same pcb, the other the one to link to other cards.


:toast:
 

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thats a confusing graph since it mentions sideport, but it makes sense.

0.9GB/s per bridge.
 

cadaveca

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Yeah, not the best, but as soon as I saw the question, I thought of it, as I'm not too sure of anywhere else where AMD has released this information. I've seen it, but cannot remember where.

Important to me, as running 2560x1600, each frame avgs...hmm..probably like 16MB, so 100FPS of frames transfered is not possible with just one bridge. Max would be around 55 FPS or so...

1920x1080 should use half that, or allow for double the frames on one interconnect.
 

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Yeah, not the best, but as soon as I saw the question, I thought of it, as I'm not too sure of anywhere else where AMD has released this information. I've seen it, but cannot remember where.

Important to me, as running 2560x1600, each frame avgs...hmm..probably like 16MB, so 100FPS of frames transfered is not possible with just one bridge. Max would be around 55 FPS or so...

1920x1080 should use half that, or allow for double the frames on one interconnect.

its quite likely related to why the lower PCI-E bandwidth isnt as killer as we thought - the most critical data goes over the bridges.
 

cadaveca

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As far as I know, only the rendered frames are sent via the bridge, and PCI-E is used for other communications...

(and how nV disables Crossfire via bios on nV chipsets...they simply disable the inter-gpu pci-e link, and the boards offer no other link{as Crossfire can use DMI as it did on P965})

...PCI-E is also used for R5xx-gen software Crossfire, which uses NO bridges, so PCI-E is MORE IMPORTANT depending on resolution used(and the app being able to run over 55FPS on a single gpu, as currently most OEMs are telling people only one bridge is required, which is not entirely true), and hardware(or lack of it, as in software Crossfire).

I tried explaining this to more than one XFX tech...they wouldn't budge on it though...still they recommend only using one bridge(seemingly as a way to curb microstutter caused by frames being sent over both connects, and causing sync issues).
 

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As far as I know, only the rendered frames are sent via the bridge, and PCI-E is used for other communications...

(and how nV disables Crossfire via bios on nV chipsets...they simply disable the inter-gpu pci-e link, and the boards offer no other link{as Crossfire can use DMI as it did on P965})

...PCI-E is also used for R5xx-gen software Crossfire, which uses NO bridges, so PCI-E is MORE IMPORTANT depending on resolution used(and the app being able to run over 55FPS on a single gpu, as currently most OEMs are telling people only one bridge is required, which is not entirely true), and hardware(or lack of it, as in software Crossfire).

I tried explaining this to more than one XFX tech...they wouldn't budge on it though...still they recommend only using one bridge(seemingly as a way to curb microstutter caused by frames being sent over both connects, and causing sync issues).

i suffered from that microstutter issue, but get it regardless of one bridge or two. go figure.

When i tested on a 16x/4x platform (PCI-E 1.1 to boot, P35) - there was zero performance difference.

I honestly beleive only one bridge can be used with two GPU's (and two bridges with three)
 

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thats a confusing graph since it mentions sideport, but it makes sense.

0.9GB/s per bridge.

Using two bridges between two cards doesn't up that to 1.8 GB/s. CFBI has a usable bandwidth of 0.9 GB/s between two GPUs.
 

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Using two bridges between two cards doesn't up that to 1.8 GB/s. CFBI has a usable bandwidth of 0.9 GB/s between two GPUs.

i know. i should have specified - i was thinking triple cards at the time.
 

cadaveca

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I honestly beleive only one bridge can be used with two GPU's (and two bridges with three)

If that was teh case, AMD wouldn'r recommend conencting both, but Catalyst driver recomends connecting both bridges, unless this is meant for bridges on both cards...
 

cadaveca

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Ah, here's another place where they say it, in the manual:

ATI CrossFireX Ready motherboard and one ATI CrossFireX Bridge Interconnect cable per graphics card (included) are required

Sry for double posting, but it's been some time since my last post, and new info is present.
 

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Very nice review! :respect: Cleared me some doubts.


both run on 8x. performance hit will be next to nothing.

1.1 or 2.0 ?????

Question:

I have one 16x 1.1 slot and other 8x 1.1 slot = (8x 2.0 / 4x 2.0), I'm thinking about to install two HD 5870 in crosffire mode, what is the final speed with this configuration, 8x or 4x 1.1? :(

tnks for the help.
 

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Hi there, first of all great post.. i am really suprised seeing some numbers. 2nd, excuse me for digging up an old thread.

Now this.. atm i own a Asus p7p55d-le which has, with 1x XFX 5770.
I wasnt planning on Crossfire, so didnt really care about the PCI-Express slots, being 16x or whatever.

Now after a while, i do wanna go Crossfire 5770.. But i am wondering how much of a performance hit i would get, because 1 slot will be PCI-Express 2.0 x16, the other one will be PCI-Express 2.0 x4 (as far as i understood, correct me if wrong)

How much of a hit would i get with 2x 5770 on a p55 board? will it be the ~5% stated in the graph, which is "nothing" or will it be (much) more?

Thanks in advance!
 
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