CPU PCIe lanes vs. Chipset PCIe lanes

[axipher]

Hey all,

 

I just ordered an Asus X570-Pro board that can run two of the PCIe x16 slots at 4.0 x8 form the CPU and the third PCIe at 3.0 x4 from the X570 chipset.

 

Alongside the x16 slots, the two M.2 slots are split between the CPU and the Chipset and all the x1 slots are from the Chipset.

 

 

I plan to run a M.2 daughter board in one of the x16 slots form the CPU so I can run two M.2 drives in UnRaid as a mirrored Cache drive both from the CPU PCIe lanes directly. I've had issues on previous Ryzen builds where the M.2 drive mirroring didn't play nicely under high load when separated across the CPU and chipset.

 

 

I also plan to run an Nvidia GPU for Plex Transcoding and a 10 Gig Mellanox card that needs 3.0 x4.

 

 

 

My question now is what is the performance hit of running the Network card off the Chipset PCIe lanes vs. the CPU lanes directly?

 

 

 

I'm pretty sure I can't run the GPU off the chipset PCIe lanes for just encoding, but I could be wrong.

[ENTERPRISE]

Hey all,

 

I just ordered an Asus X570-Pro board that can run two of the PCIe x16 slots at 4.0 x8 form the CPU and the third PCIe at 3.0 x4 from the X570 chipset.

 

Alongside the x16 slots, the two M.2 slots are split between the CPU and the Chipset and all the x1 slots are from the Chipset.

 

 

I plan to run a M.2 daughter board in one of the x16 slots form the CPU so I can run two M.2 drives in UnRaid as a mirrored Cache drive both from the CPU PCIe lanes directly. I've had issues on previous Ryzen builds where the M.2 drive mirroring didn't play nicely under high load when separated across the CPU and chipset.

 

 

I also plan to run an Nvidia GPU for Plex Transcoding and a 10 Gig Mellanox card that needs 3.0 x4.

 

 

 

My question now is what is the performance hit of running the Network card off the Chipset PCIe lanes vs. the CPU lanes directly?

 

 

 

I'm pretty sure I can't run the GPU off the chipset PCIe lanes for just encoding, but I could be wrong.

 

Hey bud,

 

I have a X570 Board, if it was a GPU question I would likely have been able to answer but it pertains to a Network Card. So we know that the Chipset lanes will inherently have some additional latency to them if you are comparing against CPU lanes BUT playing devils advocate here. We all know that latency issues when running something like a GPU or Multi-GPU has been known to be an issue if you are using a PCIE slot assigned to a CPU and the other to the Chipset. As we know GPU's are fairly sensitive to latency. HOWEVER, there is no doubt your 10G card will work fine in a slot assigned to the Chipset. I would say that any slight increase in latency from using a slot assigned to the Chipset is going to un-noticeable. Sure on paper there may be an ever slight performance issues (Possibly none at all due to the type of data traffic involved) but I cannot see it having a performance hit. Not to the point where you are like "Dude my network is so slow"

 

I personally think you will be fine assuming that after your entire config including the M.2 drives will leave you adequate lanes to run the card at its full potential.

[axipher]

Thanks the the reply. I was kind of thinking the same thing, that it would be minimal latency that would mostly mess with Crossfire/SLI or PCIe Raid (M.2 PCIe drives).

 

I'm just wondering if something like a GTX 1050 Ti will run fine for just video encode/decode for Plex on the chipset PCIe 4.0 x4 or just through the network card down there instead. The Network is more important for me, but if it's just a very tiny increase in latency, it should be fine in my mind, just wanted someone else's thoughts and potentially expertise on the issue.

[ENTERPRISE]

Thanks the the reply. I was kind of thinking the same thing, that it would be minimal latency that would mostly mess with Crossfire/SLI or PCIe Raid (M.2 PCIe drives).

 

I'm just wondering if something like a GTX 1050 Ti will run fine for just video encode/decode for Plex on the chipset PCIe 4.0 x4 or just through the network card down there instead. The Network is more important for me, but if it's just a very tiny increase in latency, it should be fine in my mind, just wanted someone else's thoughts and potentially expertise on the issue.

 

Running a Plex server myself, I can tell you that the encode/decode performance will not be affected if the GPU is in a slot assigned to the chipset. I have never had any problems, lets put it that way. If there is a performance hit, then I can say with confident you would only see it on paper and nothing that would cause you any particular performance degradation:)

[axipher]

 

Running a Plex server myself, I can tell you that the encode/decode performance will not be affected if the GPU is in a slot assigned to the chipset. I have never had any problems, lets put it that way. If there is a performance hit, then I can say with confident you would only see it on paper and nothing that would cause you any particular performance degradation:)

 

That's good news then, I might just throw my GPU in the chipset PCIe slot then and give that a test for transcoding first then.

[ENTERPRISE]

Yeah you can always test these things by swapping things out. You can try it in the Chipset controlled PCIe and then compare it when it a CPU controlled PCIe.