Are My PCIe Lanes My Bottleneck?

[kenn213]

I'm trying to determine if my PCIe lanes are a potential bottleneck in my system. First here's my relevant hardware:

• 
  Maximus VI Formula
  i7 4770k
  (2x) GTX Titan X (in 3.0 slots 1 & 2)
  Intel 750 PCIe SSD (in 3.0 slot 3)
  Creative X-Fi Titanium (in first 1.0 slot)

As I understand it my Z87 chipset only has 16 PCIe lanes, forcing my GPUs into x8/x8 mode. With the PCIe NVME SSD as well I'm curious how much of a performance gain I might see moving to X99 or Z170 chipset/processor with 40 PCIe 3.0 lanes.

 

[MarkW]

From the Asus Maximus VI Formula website:
3 x PCIe 3.0/2.0 x16 (x16 or dual x8 or x8/x4/x4) *1
1 x mini-PCIe 2.0 x1 *2
3 x PCIe 2.0 x1

So looking at your motherboard, Starting from the slot closest to your CPU, you have

PCie 2.0 x1: Creative sound card
PCie 3.0 x8: Titan X
PCie 3.0 x4: Titan X
PCie 3.0 x4: Intel SSD

So here is the problem. As soon as you put the SSD card into PCIe 3.0 slot 3, both PCIe 3.0 slot 2 and 3 become a x4 slot. So the 3 PCIe 3.0 slots become 8x/4x/4x.

SLI requires x8 for each video card. Anything less, and the any video card getting less than x8 goes into sleep mode. So in your case, the second Titan all but shuts down. It will do nothing as long as the SSD is in slot 3.

And that creates a problem because all of the remaining slots are PCIe 2.0 x1. How the SSD would perform in those slots is questionable, but PCIe 2.0 x1 is not a lot of bandwidth.

You can see all of this info on pages 1-25 and 1-26 in your motherboard users manual.

 

[kenn213]

Thanks MarkW. That is basically what I thought was happening. I wasn't sure that the SSD was forcing my slots into x8/x4/x4 mode so thanks for confirming that.

My question still is how much of a gain would I get moving to a 40 lane chipset? From what you've said it sounds like I would see significant gains with my hardware. I actually can't even enable SLI in the Nvidia Control Panel since updating to Windows 10 and I was curious if this may be part of the problem. When gaming I see my first card between 80-95% usage, and the second card is 10-20% used (I think just for Physx).

If I decide to move to a 40 lane chipset, would going for the more mature x99 or the brand new z170 make more sense at this point? Both would require a new CPU and board, however Z170 would require DDR4 from what I've been reading.

 

[MarkW]

Going to a X99 system that allows you to run with 40 PCIe 3.0 lanes will allow you to do what you are trying to do.

But! Doing that will force you to buy a new motherboard (socket 2011-v3 instead of 1150), DDR4 memory instead of the DDR3 you have now, and of course the new CPU. An i7-5960X will cost $1000+, and the only other choice with 40 lanes is the i7-5930K, which is about $550. There is a 24 lane version, I7-5820K, that runs in the $320 range I believe, but if you are going to go this route, I do recommend the 40 lane chips. You just have more long term options with the extra lanes. Not to mention being able to run both video cards now at x16 each, and still have lanes left for the SSD.

 

[kenn213]

Thanks. That clears it up for me.

So I basically have to decide if dropping a grand or two between cpu, board and ram is worth it for that upgrade.

 

[MarkW]

Yup. How much is gaming worth to you... LOL...

I suspect you will go for it, and have a great time with that machine!

Enjoy it!