PCIe Speeds finally matter, kinda

[UltraMega]

A friend of mine upgraded from a GeForce 1070 to a GeForce 3070 recently. 

 

His PC already had a sound card, and he wanted to add a wifi6 card at the same time. This meant all of the PCI slots on his PC were to be used. 

 

Short-sidededness meant the only way to fit the GPU and the two PCI cards in meant the GPU had to go into the bottom slot to physically fit, which is a PCI3 4X slot (4GBps)

 

We've all heard about how PCIe speeds don't matter for GPUs. I am here to tell you that in this case, it mattered very much. The 3070 performance under a 4X PCI3 slot was terrible. It probably tripled at least when we got the extension cables needed to move his other PCI cards lower in the case to make room for the GPU to fit into the 16x slot. Once we did that, performance was great. 

 

4X PCIe3 - massively bad performance, constant stuttering. Bad performance at 1080p

 

16X PCIe performance - totally smooth, like you would expect. Good performance at 1440p-4K

 

I wish I had recorded data. Researching this situation beforehand, I could not find any instance of a GPU as powerful as a 3070 in a PCIe slot as slow as a 4X PCIe3 slot. So this thread is just to point out that PCIe speeds are starting to matter.

[schuck6566]

This is why I'm on the fence about upgrading from my 2070 until I get a setup with pci4. If I go to the current gen cards,I'll be loosing performance because it'll be running on pcie3.

[pio]

I'll run my 6900XT on PCIe 1.0 x16 with a Socket 939.  Don't tempt me bro.....  

I definitely wish you'd have taken some recordings man, this would've been interesting information.  PCIe 3.0 x4 is basically PCIe 1.0 x16 in terms of bandwidth capabilities.  

[Sir Beregond]

Comments about PCIe not mattering usually didn't go from x16 PCIe 4 to x4 PCIe 3. That's a huge difference.

 

It's also why there was a bunch of talk around AMD using x8 on say the 6500 XT because once again there was a big difference in performance between plugging it into a PCIe 4 slot vs 3 slot over the x8 interface of the card.

 

Where you'd not see a big difference is between x16 and x8 PCIe 4.

Edited December 2, 2023 by Sir Beregond

[acoustic]

lol i feel like you took it to the absolute extreme. most people when arguing pcie speeds are talking about 4.0 x8 vs x16, or 3.0 x8 vs x16. in most cases there is no difference with 99% of GPUs

[UltraMega]

Yea I get a 4x gen 3 slot a huge step down from a 16x slot, or just a gen 4 slot, but it's still interesting just how much it hindered the card. Some games went from completely unplayable to perfectly smooth. 

 

A 3070 isn't that powerful of a card too, so just interesting that it mattered sooo much for a mid range card. 

[SoloCamo]

  On 02/12/2023 at 08:24, schuck6566 said:

This is why I'm on the fence about upgrading from my 2070 until I get a setup with pci4. If I go to the current gen cards,I'll be loosing performance because it'll be running on pcie3.

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I used a 6900XT on pci-e 3.0 16x with zero perceivable difference compared to 4.0 16x.  From my understanding, It actually matters much more when you are at / over your vram limit on your gpu and the slower bus absolutely can affect it.  I'm sure a 4090 or such would still see a performance regression going to pci-e 3.0 16x but you'd likely need a hell of a cpu to push it to that point in the first place.

Edited December 3, 2023 by SoloCamo

[bonami2]

Had no issue running my 6800xt pushing bf4 ultra 4k on an amd fx with pcie 2.0 x16

Edited December 3, 2023 by bonami2

[UltraMega]

  On 03/12/2023 at 05:25, bonami2 said:

Had no issue running my 6800xt pushing bf4 ultra 4k on an amd fx with pcie 2.0 x16

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Bf4 is an old game. I bet that would have run fine in my situation as well.