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PCI Express Headache....Requesting Assistance

Last response: in Graphics & Displays
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August 22, 2012 11:37:51 AM

Hey guys. I’ve been coming here semi-religiously since I first became seriously into enthusiast PC components/benchmarking/etc. I recall in 2011 I was having an issue enabling SLI with 2 x GTX560Ti’s and you guys helped me out almost immediately. I’ve exhausted all of my resources looking for an answer to my problem, so I decided to seek wisdom here again.

Before I lay out my question and scenario, I want you to know I understand how trivial the question is and how many of you may roll your eyes. I understand PCI Express 3.0 vs. 2.0 on benchmarks is basically no difference with the software we have today. But to the nerd in me, I do care about this. Thank you for understanding.

I can hit 2256 or above in the Heaven DX11 Benchmark 1920x1080 Max Settings, Top 20 Systems Benchmark List on passmark.com, #1 System on Performance Test v8.0 without using a RAM Disk, Si Sandra ranks me 99.6%ile…I’m not bragging I just want you guys to know I really care about this stuff. It’s a healthy hobby that I replaced a bad one with. Enough talk, I’ll get right to it.

Current Rig
ASUS P8Z77-V PRO Motherboard
Intel i7 3770k (Usually run it at 4.0GHz but can go up to 4.8/4.9GHz before BSOD)
4x4GB G-Skill Sniper DDR3 2133 RAM
2 x 120GB Mushkin Chronos Deluxe SSD in RAID 0 on the Intel SATA III Controllers
1 x 1TB Seagate 7200RPM HDD
Corsair 750W Gold PSU (Has four 6+2 PCIE Power Outputs)
Corsair H100 Liquid Cooler (Doesn’t really fit….had to rig it on top. May get a new case- Full Tower)
CoolerMaster HAF 912X case
2 x GTX 670 SLI (EVGA 2GB, Standard Model, $399 was the original price when it first came out)
Windows 7 Ultimate x64

Problem
Regardless of system stress, my GPUs report this across practically every software device I looked at:
GPU1- PCI E 3.0 @ x4
GPU2- PCI E 3.0 @ X8

The HDMI out is in the top card, GPU1. Temps are mid 30s idle, 60s under load. GPU2 has hit low 70s before but cools down extremely fast when fan profiles are tweaked to be more aggressive and after quitting the stress on the GPU. When transcoding video to a different format, I watch the statistics and the average is: CPU 20-25% Load, GPU1 11% load, GPU2 65% load.

I understand that x16/x8 is the standard for 2.0 SLI, which is sort of what I am getting now but the cards are somehow reversed. I have tried all different BIOS Settings, updating BIOS, reinstalling Windows, even reseating the CPU and GPUs (I don’t know why). My particular motherboard reports PCI Express 3.0 x 16 2(x16/0 or x8/8), PCI Express 2.0 x 16 1(@x4).

Maybe I am reading it wrong or fail to understand something. The dream would be PCI E 3.0 @ x16/x8, but 3.0 @ x8/x8 would really make me happy. I feel like I should be getting 3.0 @ x8/x8. Again, I know it really doesn’t make a difference, but I have been trying to solve this for 6 weeks with no luck. Any help you can give will not go unappreciated. Thank you all in advance!
a c 115 U Graphics card
August 22, 2012 11:57:47 AM

The Sandybridge and Ivybridge processors only have 16 PCIe lanes

Sandybridge is second generation

Ivybridge is third generation

These 3.0 lanes can be configured in the following way:

Sandybridge:

1 x 16
2 x 8

Ivy bridge:

1 x 16
2 x 8
1 x 8 & 2 x 4

If a sandybridge processor is used in a Z77 chipset which employs 3 full width slots then the third slot will not be functional.

In addition to the 16 lanes tied directly to the CPU there are up to an additional 8 lanes available from the PCH. These lanes can be used for add-in controllers, extra PCIe slots, Thunderbolt, whatever; it is up to the manufacturer.

Some 7 series motherboard manufacturers will use 2 full width slots and one quarter width slots (4x) for the CPU rather than 3 full width slots. This is for marketing purposes as it limits the use of 3 way SLI/CrossfireX to high end motherboards unless someone wants to take a hacksaw to their graphics card.

You may have a device plugged into a 4x slot that is connected directly to the CPU. This will cause your slots to run in 8/4/4 mode rather than 8/8/0 mode. You may be able to move this device to another 4x slot that is connected to the PCH instead.
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August 22, 2012 12:11:43 PM

Brother, I thank you for your fast reply. 3770k is Ivy Bridge. The P8Z77-V PRO has three PCI Express Slots. The bottom one is not a good idea to use because I would have to either use the mobo on a bench or a full tower to reach it...not to mention all the items I would have to unplug. Okay, so based on your information I only "rate" the equivalent of 2 x 8 which is what I am hoping for. I have the top slot running at x4 and the second running at x8. Nothing in the third. No other PCI items anywhere in the system.

I should note that before I purchased the second GPU I was running 3.0 @ x16 LIKE A BOSS. Not I am down to 3.0 @ x4 and 3.0 @ x8. If it was the other way around I would understand it to be 2.0 @ x16/ 2.0 @ x8 just like you are saying with Ivy.

Taking your information into my head, I must now ask why do you think the "master" GPU is running at x4 and the other at x8? According to the Motherboard specifications, all I am using are PCI Express16_1 and PCI Express16_2. There is a third one but I have nothing in it. There is also x4 PCI slots and old school PCI slots but they are idle with no hardware attached.
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a c 115 U Graphics card
August 22, 2012 12:23:29 PM

If you have nothing else in the system then you should be getting 8x/8x at 3.0 speeds.

My guess is that the SLI connector and weight of the second card may be pulling the top card down and preventing one or more pins from making contact. I had this exact problem with some watercooled EVGA GTX 280s a couple of years ago.

Since PCIe negotiates the link width based on the presence of sense pins which may be shortened to ensure full contact of all datapins first (PCIe is hotswappable) it's possible that one of these shortened pins is not making contact. On many boards only the last sense pin is shortened

for reference: http://en.wikipedia.org/wiki/PCIe

If you look at your card you'll notice that on the top pin 81 may be shortened (component side, cards are inserted upside down or solder side up). Pin 48, 31, and 17 may be shortened as well. These correspond to 16x,8x,4x, and 1x width connection compatibility.

Since these pins are on the top of the board they may lose contact if the board is tugged downward. Try applying some upward pressure on the cards to keep them in place
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August 22, 2012 12:27:57 PM

Pinhedd said:
If you have nothing else in the system then you should be getting 8x/8x at 3.0 speeds.

My guess is that the SLI connector and weight of the second card may be pulling the top card down and preventing one or more pins from making contact. I had this exact problem with some watercooled EVGA GTX 280s a couple of years ago.

Since PCIe negotiates the link width based on the presence of sense pins which may be shortened to ensure full contact of all datapins first (PCIe is hotswappable) it's possible that one of these shortened pins is not making contact. On many boards only the last sense pin is shortened

for reference: http://en.wikipedia.org/wiki/PCIe

If you look at your card you'll notice that on the top pin 81 may be shortened (component side, cards are inserted upside down or solder side up). Pin 48, 31, and 17 may be shortened as well. These correspond to 16x,8x,4x, and 1x width connection compatibility.

Since these pins are on the top of the board they may lose contact if the board is tugged downward. Try applying some upward pressure on the cards to keep them in place


I will try this immediately upon returning home from work and report back. Thank you very much!
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a c 115 U Graphics card
August 22, 2012 12:33:13 PM

RelentlessFury said:
I will try this immediately upon returning home from work and report back. Thank you very much!


You're welcome. Good luck and have fun!
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