Sandy-E, x79 and SLI

[Zarathustra[H]]

hey all,

I'd like to see what I can learn from your experience in all this.


With an x79 Sandy-E system, does it make sense to use Nvidia's "force-enable-gen3.exe" to enable PCIe 3.0?

At first I thought "of course", but I have been seeing a lot of erratic frame times in game, with my two 980ti's in SLI, and I'm wondering if this is the cause, especially since the high frame times seem to not be related to GPU load (I'm adaptive vsynced at 60fps and 4k in some titles with as little as 60% GPU load when it happens)

The reason I am suspecting that this might be the problem is this quote from the link above:

GeForce GTX 680 and GTX 670 GPUs support PCI Express 3.0. They operate properly within the SIG PCI Express Specification and have been validated on multiple PCI Express 3.0 platforms. Some motherboard manufacturers have released an updated SBIOS to enable the Intel X79/SNB-E PCI Express 2.0 platform to run at up to 8GT/s bus speeds. We have tested GeForce GTX 680 and GTX 670 GPUs across a number of X79/SNB-E platforms at 8GT/s bus speeds, but have seen significant variation in signal timing across different motherboards and CPUs. Therefore we’ve decided to only support and guarantee PCI Express 2.0 bus speeds on X79/SNB-E with our standard release drivers. Native PCI Express 3.0 platforms (like Ivy Bridge) will run at 8GT/s bus speeds with our standard release drivers.

Do you guys think it would be better to drop down to PCIe 2.0?

I know that in the past PCIe bus speed has not been seen as a major impact on performance,but it's been a while since those tests were performed. Would PCIe 2.0 even be sufficient to support two 980Ti's in SLI at 16x-16x?

Appreciate any thoughts on this subject.

--Matt

 

[jedimasterben]

A PCI-E gen3 slot at x8 has the same bandwidth as a gen2 slot at x16, and it won't have any noticeable impact on performance.

 

[Zarathustra[H]]

A PCI-E gen3 slot at x8 has the same bandwidth as a gen2 slot at x16, and it won't have any noticeable impact on performance.

I assumed that would be the case, but I wanted to check to make sure.

Do you think my suspicions regarding the timing issues Nvidia mentions with PCIe 3.0 on x79 being related to frame time irregularities might be true?

(I am going to test either way, and report back, I just might not get to it right away.)

 

[BroHamBone]

I use force enable gen3 w/ my x79 board. Im running SLI at the moment also. But as a previous poster mentioned, the difference between x8 3.0 and x16 2.0 is pretty much negligible. I think I ran a single card in x8 3.0 vs x16 2.0 on firestrike and the overall score was maybe 120 points, give or take.

 

[Zarathustra[H]]

I use force enable gen3 w/ my x79 board. Im running SLI at the moment also. But as a previous poster mentioned, the difference between x8 3.0 and x16 2.0 is pretty much negligible. I think I ran a single card in x8 3.0 vs x16 2.0 on firestrike and the overall score was maybe 120 points, give or take.

Yeah, I am currently running 16x-16x in PCIe 2.0 mode on my X79 system.

In order to do so I had to pull out my 10gig ethernet adapter when I installed the second 980ti.

I am considering putting in back in, getting an Intel 750 PCIe SSD and forcing 3.0 mode at 8x-8x instead. It should theoretically have about the same bandwidth, and all the tests I seen indicate that framerates are indistinguishable from eachother, but I ahve yet to see anyone compare frame times.

The reason I am concerned about frametimes is because frametimes cause stutter, which doesn't necessarily show up in FPS or Firestrike scores.

On most systems I wouldn't be concerned, but I am concerned on my x79 system because of Nvidia's statement about why they leave x79 systems in PCIe 2.0 mode by default:

GeForce GTX 680 and GTX 670 GPUs support PCI Express 3.0. They operate properly within the SIG PCI Express Specification and have been validated on multiple PCI Express 3.0 platforms. Some motherboard manufacturers have released an updated SBIOS to enable the Intel X79/SNB-E PCI Express 2.0 platform to run at up to 8GT/s bus speeds. We have tested GeForce GTX 680 and GTX 670 GPUs across a number of X79/SNB-E platforms at 8GT/s bus speeds, but have seen significant variation in signal timing across different motherboards and CPUs. Therefore we’ve decided to only support and guarantee PCI Express 2.0 bus speeds on X79/SNB-E with our standard release drivers. Native PCI Express 3.0 platforms (like Ivy Bridge) will run at 8GT/s bus speeds with our standard release drivers.

I don't want to go out there and order a almost $400 750 SSD, only to find out that when enable PCIe 3.0 and go from 16x-16x to 8x-8x - even though every review out there says framerates are unaffected - frametimes ARE affected due to the signal timing issues Nvidia mentions above.