Using PCIe 2.0 x1 Slots

[sandals100]

Hey Guys,

 

So I've recently gotten into mining and have truly realsied how confusing it is. I've currently got 2 R9 290x's and love it. Its running on a Asrock AB350 Pro 4 motherboard with a Ryzen 3 1200. I was looking around and noticed people using some sort of riser to also utilize the smaller slots (circled in the picture) to connect more cards. I wasn't sure if this was a bitcoin section question or a motherboard question but my apologies if it is wrong.

 

My question is if there is any downfall to getting risers and doing it that way and if the cpu is capable in terms of lanes etc?

 

 

 

Thanks

[Jurrunio]

I'm not sure if there's even a question

[BlueChinchillaEatingDorito]

There's less bandwidth available to your cards if you use those slots as those are PCI-E 1x electrically. I don't know how much that'll affect your mining since I don't do any of that stuff. 

[3rrant]

11 minutes ago, sandals100 said:

Hey Guys,

 

So I've recently gotten into mining and have truly realsied how confusing it is. I've currently got 2 R9 290x's and love it. Its running on a Asrock AB350 Pro 4 motherboard with a Ryzen 3 1200. I was looking around and noticed people using some sort of riser to also utilize the smaller slots (circled in the picture) to connect more cards. I wasn't sure if this was a bitcoin section question or a motherboard question but my apologies if it is wrong.

 

 

 

Thanks

 

7 minutes ago, BlueChinchillaEatingDorito said:

There's less bandwidth available to your cards if you use those slots as those are PCI-E 1x electrically. I don't know how much that'll affect your mining since I don't do any of that stuff. 

PCI-E bandwidth do not increase or reduce mining performance. Most of the performance gain are based on the memory type and its clock. Relatively the clock speed of the GPU itself can increase or decrease performance, but mainly affects power consumption and heat (for mining).

 

"Risers" are used to plug several GPUs in a single system. They connect to the x1 slot on one side and on the x16 slot on the card side. This is the case if you don't need to also power the card itself with the riser because you are going to use the PSU cables for it. There are longer risers that both power the card (taking power from a molex, usb or other connectors) and transmit signals.

[sandals100]

1 hour ago, Jurrunio said:

I'm not sure if there's even a question

Edited it my mistake.

 

1 hour ago, BlueChinchillaEatingDorito said:

There's less bandwidth available to your cards if you use those slots as those are PCI-E 1x electrically. I don't know how much that'll affect your mining since I don't do any of that stuff. 

Yeah I read up on a bit but I couldn't really wrap my head around it.

 

1 hour ago, ErrantNyles said:

 

PCI-E bandwidth do not increase or reduce mining performance. Most of the performance gain are based on the memory type and its clock. Relatively the clock speed of the GPU itself can increase or decrease performance, but mainly affects power consumption and heat (for mining).

 

"Risers" are used to plug several GPUs in a single system. They connect to the x1 slot on one side and on the x16 slot on the card side. This is the case if you don't need to also power the card itself with the riser because you are going to use the PSU cables for it. There are longer risers that both power the card (taking power from a molex, usb or other connectors) and transmit signals.

 

Oh okay, will the CPU have enough lanes for a 3rd gpu?

[Jurrunio]

34 minutes ago, sandals100 said:

Oh okay, will the CPU have enough lanes for a 3rd gpu?

Consumer CPUs have 16 lanes, so you can use 16 cards if you are willing to use PCIe x16 splitters.

[3rrant]

54 minutes ago, sandals100 said:

Edited it my mistake.

 

Yeah I read up on a bit but I couldn't really wrap my head around it.

 

 

Oh okay, will the CPU have enough lanes for a 3rd gpu?

 

17 minutes ago, Jurrunio said:

Consumer CPUs have 16 lanes, so you can use 16 cards if you are willing to use PCIe x16 splitters.

As he said, yes.

 

There are other ways to "increase" lanes, which might or not reduce bandwitdh for 16+ cards.

[Sakkura]

59 minutes ago, sandals100 said:

Edited it my mistake.

 

Yeah I read up on a bit but I couldn't really wrap my head around it.

 

 

Oh okay, will the CPU have enough lanes for a 3rd gpu?

The PCIe 2.0 x1 slots are not using lanes from the CPU, they are hooked up to the B350 chipset. So there's no contention for PCIe lanes.

22 minutes ago, Jurrunio said:

Consumer CPUs have 16 lanes, so you can use 16 cards if you are willing to use PCIe x16 splitters.

This is not correct. Not only are there lanes both from the CPU and the chipset, but the CPU lanes also cannot be split individually as you suggest.

[Jurrunio]

6 minutes ago, Sakkura said:

The PCIe 2.0 x1 slots are not using lanes from the CPU, they are hooked up to the B350 chipset. So there's no contention for PCIe lanes.

This is not correct. Not only are there lanes both from the CPU and the chipset, but the CPU lanes also cannot be split individually as you suggest.

Really?

Then how can multi GPU setups work if CPU lanes cant be split?

[Sakkura]

8 minutes ago, Jurrunio said:

Really?

Then how can multi GPU setups work if CPU lanes cant be split?

The CPU lanes can be split to x8/x8 by the X370 chipset (the B350 chipset in OP's board doesn't even allow that). Intel's Z270 chipset can split the 16 PCIe lanes from those CPUs to x8/x4/x4. But splitting the CPU lanes up individually isn't possible on any mainstream platform on the market.

 

The PCIe lanes from the chipset are usually more flexible in that regard, though.

[Jurrunio]

2 hours ago, Sakkura said:

The CPU lanes can be split to x8/x8 by the X370 chipset (the B350 chipset in OP's board doesn't even allow that).

But B350 (and OP's mobo) does support Crossfire.

[Lurick]

10 minutes ago, Jurrunio said:

But B350 (and OP's mobo) does support Crossfire.

Crossfire only needs x4 to work, SLI needs x8 to work.

[SpaceGhostC2C]

6 minutes ago, Jurrunio said:

But B350 (and OP's mobo) does support Crossfire.

It is not "splitting", though, but rather the way it's  wired: the slots are "wired" (that is, the traces on the PCB) so that they can work as 16x or 8x. The switching happens automatically as you plug devices into the slots. For B350, there are motherboards wited in different ways, meaning different things get disabled as you plug others, and you can achieve different combinations of hardware. 

In any case, you cannot achieve any configuration that was not originally wired in the motherboard. 

[Sakkura]

19 minutes ago, Jurrunio said:

But B350 (and OP's mobo) does support Crossfire.

Not SLI though, which tells you the cards are not both getting 8 lanes (that's what Nvidia requires, while AMD is less strict).

 

What's really happening is that the first GPU is getting the full 16-lane connection. The second GPU then "steals" lanes elsewhere - either the PCIe 3.0 x4 from the CPU intended for an M.2 NVMe SSD, or PCIe 2.0 lanes from the chipset.

 

In OPs case, the Asrock AB350 Pro4 runs the second GPU off the PCIe 3.0 x4 for M.2. That's why they have this footnote in the specs:

 

Quote

AMD Ryzen series CPUs
- 2 x PCI Express 3.0 x16 Slots (single at x16 (PCIE2); dual at x16 (PCIE2) / x4 (PCIE4))*
AMD 7^th A-Series APUs
- 2 x PCI Express 3.0 x16 Slots (single at x8 (PCIE2); dual at x8 (PCIE2) / x2 (PCIE4))*

- 4 x PCI Express 2.0 x1 Slots
- Supports AMD Quad CrossFireX™ and CrossFireX™**
 

*Supports NVMe SSD as boot disks
If M2_1 is occupied, PCIE4 will be disabled.

(I underlined the relevant parts)

[Jurrunio]

54 minutes ago, SpaceGhostC2C said:

It is not "splitting", though, but rather the way it's  wired: the slots are "wired" (that is, the traces on the PCB) so that they can work as 16x or 8x. The switching happens automatically as you plug devices into the slots. For B350, there are motherboards wited in different ways, meaning different things get disabled as you plug others, and you can achieve different combinations of hardware. 

In any case, you cannot achieve any configuration that was not originally wired in the motherboard. 

So it's the wiring that controls the distribution of CPU lanes, so mining boards with a lot of PCIe x1 / x4 slots work because of special wiring?

[SpaceGhostC2C]

11 minutes ago, Jurrunio said:

So it's the wiring that controls the distribution of CPU lanes, so mining boards with a lot of PCIe x1 / x4 slots work because of special wiring?

I'm not sure, but I don't think you even need the GPUS to be connected to PCIe lanes directly from the CPU for mining. Many mining rigs use USB to PCIe adapters to hook cards. Given that mining seems to depend little on bandwidth, it shouldn't be a problem to route the communications through the chipset (4x connection to the CPU), which then acts as a hub.

 

I mean, one way or another, yes, those specialized motherboards work because all those slots are fed properly from the available lanes in terms of PCB traces.

[Mira Yurizaki]

Ohai, is it too late to do a shameless plug again?

 

2 hours ago, Jurrunio said:

So it's the wiring that controls the distribution of CPU lanes, so mining boards with a lot of PCIe x1 / x4 slots work because of special wiring?

No. The CPU figures it out on boot how to distribute the lanes it has to the devices. If you have two x16 slots meant for a multi-GPU setup and you plug in an x1 card in one of those slots, the CPU will figure this out and set it up in an x8/x8 (or maybe x8/x1) configuration. And yes, it will do that, because you can only distribute lanes in a power of two.