Article [PCGH via Neowin] PCIe 3.0 could be crippling AMD's RX 5500 XT performance

[Hitman928]

PCIe 3.0 could be crippling AMD's RX 5500 XT performance

While the bandwidth provided by PCIe 3.0 is found to be sufficient for most GPUs with adequate VRAM, the 4GB Radeon RX 5500 XT is found to be struggling possibly due to its PCIe x8 limitation.

www.neowin.net

PCI-E 3.0 vs. PCI-E 4.0: Was bringt PCI-Express 4.0 mit einer RX 5500 XT wirklich?

Welche Vorteile bietet PCI-Express 4.0 wirklich? PCGH hat eine RX 5500 XT getestet und die Ergebnisse sind beeindruckend!

www.pcgameshardware.de

PCGH is the source of the benchmarks but since it's not in english, I'm linking a write-up on the findings as well.

This story popped up in my feed, not too sure what to think of it yet and don't have much free time to really dig into it but very interesting if true. Possibly could be a driver issue at work? I don't know, it seems like PCIe3 8x shouldn't be this restricting but maybe it is.

 

[Shivansps]

AMD did not cheap out anything, these RX5500XT are actually RX460/RX560 replacements, that also had a x8 PCI-E link.

What is actually wrong is that AMD attempts to sell these as a RX580 replacement.

They also forcebly removed PCI-E 4.0 support from non x570 boards and has been half a year with no replacements in sight. So... you want to fuly use a RX5500XT 4GB? buy a x570.

 

[Golgatha]

There's no story here. These are heavy VRAM games performing better when the 5500 XT's 4GB of onboard VRAM is exceeded. The game is having to swap textures to system RAM and the interface to system RAM then becomes the bottleneck when transferring data to the video card. This is exactly analogous to when programs fill up system RAM and your HDD/SSD/NVMe drive becomes the performance bottleneck because that's where the swap file for system RAM resides.

 

[Guru]

I think he meant 5500XT 8GB vs 5700.It's odd that 8GB indeed gets benefit from PCIe 4 while 5700 doesn't.

Its not odd at all. RX 5700 has all pci-e lanes in it. The RX 5500 DOESN'T, because of a cost cutting decision by amd. RX 5700 therefore performs exactly the same at pci-e 3 or pci-e 4.

Again its only the 5500xt that doesn't have full 16x pci-e lanes due to AMD cutting 8 of them for cost savings reasons. Reason why pci-e 4 performs better is because even at 8x pci-e it has the same amount of bandwidth as pci-e 3 16x.

 

[PhonakV30]

Its not odd at all. RX 5700 has all pci-e lanes in it. The RX 5500 DOESN'T, because of a cost cutting decision by amd. RX 5700 therefore performs exactly the same at pci-e 3 or pci-e 4.

Again its only the 5500xt that doesn't have full 16x pci-e lanes due to AMD cutting 8 of them for cost savings reasons. Reason why pci-e 4 performs better is because even at 8x pci-e it has the same amount of bandwidth as pci-e 3 16x.

Here you go :

PCI-Express 4.0 Performance Scaling with Radeon RX 5700 XT

PCI-Express 4.0 has been one of the main new features prominently brandished on the product boxes of both the 3rd generation Ryzen desktop processors and Radeon RX 5700 series graphics cards. We examine the performance impact of running these cards on older generations of PCIe.

www.techpowerup.com

at 4K settings , different between PCIe 2.0 and 3.0 is 1% but 5500XT 8GB , It gets more than 1%.average is around 5%.
The Point is that , this card does have 8GB and PCIe 3.0 x8 mode ( aka PCIe 2.0 x16 mode) and Benchmark shows it gets better fps up to 10% , This means even at PCIe 2.0 x16 mode still needs to swap textures to system RAM But I don't see this absurd thing in 5700XT If you set to PCIe 2.0 x16 mode.

 

[VirtualLarry]

at 4K settings , different between PCIe 2.0 and 3.0 is 1% but 5500XT 8GB , It gets more than 1%.average is around 5%.
The Point is that , this card does have 8GB and PCIe 3.0 x8 mode ( aka PCIe 2.0 x16 mode) and Benchmark shows it gets better fps up to 10% , This means even at PCIe 2.0 x16 mode still needs to swap textures to system RAM But I don't see this absurd thing in 5700XT If you set to PCIe 2.0 x16 mode.

That's why I suspect that the issue is some sort of driver "pacing" or otherwise, latency-related issue, when transferring data via PCI-E DMA to/from the GPU's framebuffer. I don't think that it's down to bus bandwidth alone, otherwise, why wouldn't we see it with the RX 5700(XT) in PCI-E 2.0 x16 mode?

 

[NTMBK]

Bear in mind that AMD's own laptop chip only has x8 lanes for the GPU. It's a power optimization as well as a cost reduction.

 

[Thunder 57]

I recently noticed my GeForce GT 730 is PCIE 2 x8.

When these PCIE x8 GPUs get put on a expansion card, the fingers are still x16 length. [A real PCIE x8 card] So, they don't gain motherboard compatibility. Board partners lazy? Buyers think x8-length card is inferior?

I don't think I've ever seen a PCIe 8x slot. Heck, these days it seems to all be x16 and x1.

 

[Golgatha]

I don't think I've ever seen a PCIe 8x slot. Heck, these days it seems to all be x16 and x1.

You get some weird ones on server boards like that. I have a Supermicro board with an 8x physical and 4x electrical. Those are more for PCIe storage or RAID cards though.

 

[DeathReborn]

I don't think I've ever seen a PCIe 8x slot. Heck, these days it seems to all be x16 and x1.

Here is one for you. Even though it is electrically a x4 slot.

ASRock Rack > X470D4U

www.asrockrack.com