Thursday, December 22nd 2011

PCI Express 3.0 Has Zero Performance Incentive for Radeon HD 7970: Tests

Over the last few months, motherboard manufacturers have been raising a big hoopla over how it's important to pick their products that feature PCI Express 3.0 (Gen 3.0) slots. There was even some drama between competing motherboard manufacturers over who was first to the market with this technology, even when consumers couldn't really make use of the technology. To begin with, you needed a next-generation Ivy Bridge CPU, then you needed a compliant graphics card. Sandy Bridge-E, fortunately, formally introduced the technology, complete with motherboards and processors that support it.

GPU maker AMD wanted to be the first to be out there with a GPU that's compliant with this interface, and so one thing led to another, and VR-Zone got to set up a test-bed using Core i7 "Sandy Bridge-E", ASUS Rampage IV Extreme (which allows users to change PCI-Express standard mode in the BIOS setup program, by forcing Gen 2 or Gen 1 mode), and an HD 7970, to see if running the GPU on PCIe 2.0 and PCIe 3.0 modes made any worthwhile difference. The results are in: zero, nada, zilch, sunna (zero in my language).

In its comparison, VR-Zone put the GPU through 3DMark 11 (a DirectX 11 graphics benchmark) and ComputeMark (a GPU compute shader benchmark that heavily loads system bus). The performance figures between the two were agonizingly insignificant. 3DMark 11 and ComputeMark are tell-tale tests of whether the GPU (and with it, its system interface) is at least getting loaded enough. You would much rather spend the money you saved to upgrade your current, perfectly-functional LGA1155 motherboard to an "ooh-Gen3" one, on a memory upgrade, before DRAM prices rebound.



One area, however, where Gen 3.0 could have a performance incentive, could be with future Ivy Bridge LGA1155 platforms, where to run 2-way CrossFire, the single x16 link from the CPU is split into two PCI Express 3.0 x8 links. Those numbers could be interesting.Source: VR-Zone
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44 Comments on PCI Express 3.0 Has Zero Performance Incentive for Radeon HD 7970: Tests

#1
loleafidas
The current GFX can't use maximum bandwidth of PCIE 2.0, so how can they make a difference on PCIE 3.0?
Posted on Reply
#2
laszlo
by: loleafidas
The current GFX can't use maximum bandwidth of PCIE 2.0, so how can they make a difference on PCIE 3.0?
they can in your pocket....e-peen had sometimes a major buying decision :laugh:
Posted on Reply
#3
SteelSix
Yeah this one was an e-peen festival from the manufacturer standpoint; they were lining up to compare peen's while we were like WTF, another same model board? What's the difference?
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#4
Hayder_Master
I think nvidia will be work on that, other thing i see 7990 will use pci-e 3.0
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#5
Live OR Die
There probably using a old bios 1005 which isn't released on the asus website has

update microcode, pcie gen 3.0 codes

Which are probably needed.
Posted on Reply
#6
Over_Lord
News Editor
yet again if HD7970 wouldn't have supported PCIe 3.0, it would have definitely gone into the negatives of many reviews.
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#7
R_1
Don't know if it is fair comparison, because SandyBridge CPU has only 16 PCIe lines for external GPU, where SB-E got 40 PCIe lines. So ASUS probably hardwired them as 1x16 + 3x8 in Z79. That configuration benefits old PCIe 2.0, because 1x16 graphics slot has always 16 PCIe lines connected to it, where SandyBridge mobo will implement for primary graphics only 8 PCIe wired lines + another 8, by switching IC, if another external GPU is nod conected. If that switching IC is Gen2, then it cann't operate in PCIe 3.0 CPU environment and no additional 8 PCIe can be added.
Posted on Reply
#9
Grings
by: btarunr
One area, however, where Gen 3.0 could have a performance incentive, could be with future Ivy Bridge LGA1155 platforms, where to run 2-way CrossFire, the single x16 link from the CPU is split into two PCI Express 3.0 x8 links
This is the only situation i was expecting any improvement in anyway
Posted on Reply
#10
punani
um.. anandtech says otherwise:
Simply enabling PCIe 3.0 on our EVGA X79 SLI motherboard (EVGA provided us with a BIOS that allowed us to toggle PCIe 3.0 mode on/off) resulted in a 9% increase in performance on the Radeon HD 7970. This tells us two things: 1) You can indeed get PCIe 3.0 working on SNB-E/X79, at least with a Radeon HD 7970, and 2) PCIe 3.0 will likely be useful for GPU compute applications, although not so much for gaming anytime soon.
Posted on Reply
#11
repman244
by: punani
um.. anandtech says otherwise:
However that is only the case with GPU computing and not with gaming AFAIK.
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#12
Aleksander
I dont really think this is true
See the facts:
PCI-express 2 has at max 80GT/s
The card itself has 137GT/s
It can be an asus program failure too or bad programming
Look at pci-express and make a difference with 7970 in gpu-z
http://en.wikipedia.org/wiki/PCI_Express
Posted on Reply
#14
DanTheBanjoman
Señor Moderator
by: Aleksander Dishnica
I dont really think this is true
See the facts:
PCI-express 2 has at max 80GT/s
The card itself has 137GT/s
It can be an asus program failure too or bad programming
And all that data has to go over the bus? I don't think so.

It's no surprise, new standards never get utilized right away. They simply have to be there for companies to adopt and later on they will have added value. Same was true for PCI to AGP (banshee PCI or AGP, which is faster?), then to various AGP standards and then AGP vs PCIe, then PCIe 2.0 and now 3.0. All I can say is "doh".
Posted on Reply
#15
Aleksander
So you mean that the card is not giving its full potential?
Because of the bus?
Posted on Reply
#16
sneekypeet
Unpaid Babysitter
I bet MSI would argue these findings....there had to be some reason to slam Gigabyte as hard as they did when they called them out for not having it, like it was the end of PCI-e tech as we knew it without 3.0 on a board:roll:
Posted on Reply
#17
DanTheBanjoman
Señor Moderator
by: Aleksander Dishnica
So you mean that the card is not giving its full potential?
Because of the bus?
No, I'm saying it's not sending the amount of data you list over the bus. Thus it is not relevant.
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#19
R_1
People are reporting 24% difference in Mediashow Expresso between PCIe 2 and 3 mode on Z79, so here it is. :laugh:
Posted on Reply
#20
red-die
PCI-E a AGP?

dudes...guys... bro...

pci-e is not for GC only
so the development are not for GC exclusive

GC has been always have the best performance when the standard become common
not as a pioneer in pushing it

so the 1st pci-e 3.0 gc?
its like moving from a cramped apartment to a big mansion,
so much space now but it will get filled later on'
Posted on Reply
#21
Legacy-ZA
This will be very handy when you start running 4x GFX Cards in SLi / Crossfire.
Posted on Reply
#22
theeldest
Also, most users have "mainstream" systems (sandybridge). I'd imagine the difference between 2.0 and 3.0 has more of an impact when your 16 lanes are cut to 8 per card in dual-GPU setups.

And as a couple people already mentioned, makes a significant difference in compute.
Posted on Reply
#23
INSTG8R
by: loleafidas
The current GFX can't use maximum bandwidth of PCIE 2.0, so how can they make a difference on PCIE 3.0?
Pretty much my comment on it. Pure marketing nothing more...
Posted on Reply
#24
cadaveca
My name is Dave
No CPU out there actually supports PCIe 3.0, so why is this discussion even taking place? I can set my SB-E CPU to PCIe 3.0, sure...but does it work? NO!!!

So, the tech is not enabled fully, and you got no performance increase. Well, blow me over, I cannot imagine why. :rolleyes:


Where can PCIe 3.0 be used, currently? INTER-GPU COMMUNICATION. Crossfire, with multiple cards. Higher bandwidth for inter-GPU communication is needed, period.


:shadedshu
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