How does CPU ryzen 5900x or ryzen 5950x utilize PCIe Lanes on mother board?

[Orian Pax]

i am planning on getting Asus Dark Hero,
Ryzen 5950x has 20 PCIe lanes then i was wondering if it will be able to run GPU (2080ti) in x16 mode while gaming?
if
i have used all M.2 slots (one M.2 is purely windows and other one is purely linux mint, ext4 format)
1 PCIe x4 slot (chipset connected slot) used for 10 gig networking card
1 PCIe x1 slot used for sound card

okay if u don't know about above then can you point me to the place from where i can start to understand how CPUs use PCIe lanes?

it will be a big help!


DARK HERO MANUAL - https://dlcdnets.asus.com/pub/ASUS/mb/SocketAM4/ROG_CROSSHAIR_VIII_DARK_HERO/E17453_ROG_CROSSHAIR_VIII_DARK_HERO_UM_V2_WEB.pdf


 

[Electronics Wizardy]

Yup the gpu will furn a at x16 from the gpu, the top m.2 will be running with x4 from the cpu, and everything else usese the chipset lanes.

[Orian Pax]

4 minutes ago, Electronics Wizardy said:

Yup the gpu will furn a at x16 from the gpu, the top m.2 will be running with x4 from the cpu, and everything else usese the chipset lanes.

YESSSS! thanks for confirming.
another query (asking it to be just sure)

second case
Ryzen 5950x has 20 PCIe lanes then i was wondering if it will be able to run GPU (2080ti) in x16 mode while gaming?
if
i have used all M.2 slots (one is windows and other one is ntfs,storage)
1 PCIe x4 slot (chipset connected slot) used for 10 gig networking card
1 PCIe x1 slot used for sound card


can u explain a bit more how a cpu, here 5900x/5950x, which handles 20 PCIe lanes how can it handle these many lanes doesn't in the end those Chipset lanes meet CPU?
what if i am gaming and also copying files from second M.2 to the first M.2 (in background),
then will my GPU be still running in x16 mode?

And thanks for replying,sir.

[Electronics Wizardy]

4 minutes ago, Kpp550 said:

can u explain a bit more how a cpu, here 5900x/5950x, which handles 20 PCIe lanes how can it handle these many lanes doesn't in the end those Chipset lanes meet CPU?

The top m.2 and the top 2 x16 slots all run from the cpu. Everything else runs from the chipset. You gpu will always run at x16(maybe lower to save power at idle). It will never go lower when other devices are in use.

[SpaceGhostC2C]

13 minutes ago, Kpp550 said:

can u explain a bit more how a cpu, here 5900x/5950x, which handles 20 PCIe lanes how can it handle these many lanes doesn't in the end those Chipset lanes meet CPU? 

This is how your PCIe lanes work:

Spoiler

1 - As you can see at the top, there are 16 PCIe lanes going to (up to) 2 physically x16 slots (smaller than full ATX boards may not have the second x16 slot). At least 8 of those go to the top slot, and the other 8 go either to the same slot (totaling 16) or to the second x16 slot (if it's occupied). There is no other possible use for those 16 lanes.

2 - Continuing downwards, another 4 lanes go to an M.2 slot. Those are independent from the first 16.

3 - Finally, at the end (connecting the CPU and the x570 chipset in the diagram) you have 4 more lanes. Those handle the communication between the CPU and anything connected to a slot wired through the chipset. Therefore, no device in those slots can exceed the bandwidth provided by 4 lanes, and when more than one device is used at the same time, the total bandwidth is limited to the lowest of a) the connection between the device and the chipset, b) the 4 lanes connecting the chipset and the CPU. Notice that the chipset acts as a hub: it doesn't matter how many things are plugged in, you can theoretically use all 4 lanes for any individual device, provided it's the only one active at that time. For example, PCIEX16_3 in the diagram has an x8 connection to the chipset, so it could potentially saturate all 4 lanes to the CPU, if the other devices are idling. The M.2_2 slot, however, has a maximum of 2 lanes to the chipset (when nothing is plugged in the PCIEx1 slot), so regardless of how idling everything else is, it will never have more than the bandwidth of 2 lanes to the CPU.

[-rascal-]

20 minutes ago, Kpp550 said:

YESSSS! thanks for confirming.
another query (asking it to be just sure)

second case
Ryzen 5950x has 20 PCIe lanes then i was wondering if it will be able to run GPU (2080ti) in x16 mode while gaming?
if
i have used all M.2 slots (one is windows and other one is ntfs,storage)
1 PCIe x4 slot (chipset connected slot) used for 10 gig networking card
1 PCIe x1 slot used for sound card


can u explain a bit more how a cpu, here 5900x/5950x, which handles 20 PCIe lanes how can it handle these many lanes doesn't in the end those Chipset lanes meet CPU?
what if i am gaming and also copying files from second M.2 to the first M.2 (in background),
then will my GPU be still running in x16 mode?

And thanks for replying,sir.

 

The Ryzen CPU provides 20 PCI-E 4.0 lanes (16 + 4).

The 16 PCI-E lanes for graphics card is connected to PCI-E X16 slot #1 and #2.

The remaining 4 PCI-E lanes is DEDICATED for the top M.2 slot (M2_1)

The other M.2 slots (e.g. M2_2) gets its 4 PCI-E 4.0 lanes from the X570 chipset.

PCI-E X1 slots are also from the X570 chipset.

 

With your set-up (in the order as you see it physically on the board, top to bottom)

• Top M.2 slot for NVMe SSD -- 4 PCI-E 4.0 lanes from Ryzen CPU
• Top PCI-E X16_1 slot for your GPU -- 16 PCI-E 4.0 lanes from Ryzen CPU
• (Second PCI-E X16_2 slot is unused)
• PCI-E X1 slot for your network card -- 1 PCI-E 4.0 lane from X570 motherboard chipset
• Bottom M.2 slot for your Linux SSD -- 4 PCI-E 4.0 lanes from X570 motherboard chipset
• Third PCI-E X16_3 slot for network card -- 4 PCI-E 4.0 lanes from X570 motherboard chipset

 

PCI-E X16_1 and PCI-E X16_2 slots share the 16 PCI-E lanes from the Ryzen CPU.

If you put your network card into the second slot, the 16 lanes are split into 8 + 8.

 

 

[Orian Pax]

11 hours ago, -rascal- said:

If you put your network card into the second slot, the 16 lanes are split into 8 + 8.

• Top M.2 slot for NVMe SSD -- 4 PCI-E 4.0 lanes from Ryzen CPU
• Top PCI-E X16_1 slot for GPU -- 16 PCI-E 4.0 lanes from Ryzen CPU
• (Second PCI-E X16_2 slot is unused)
• PCI-E X1 slot for sound card -- 1 PCI-E 4.0 lane from X570 motherboard chipset
• Bottom M.2 slot for Linux SSD -- 4 PCI-E 4.0 lanes from X570 motherboard chipset
• Third PCI-E X16_3 slot for network card -- 4 PCI-E 4.0 lanes from X570 motherboard chipset
  (i have changed a small bit in setup, instead of network card in x1 slot now it's a sound card.)
  i see,
  so i have to go with above setup in order to keep my GPU slot from splitting in x8 + x8.
  
  Thank you very much, this solves everything.

[SpaceGhostC2C]

2 hours ago, Kpp550 said:

• Top M.2 slot for NVMe SSD -- 4 PCI-E 4.0 lanes from Ryzen CPU
• Top PCI-E X16_1 slot for GPU -- 16 PCI-E 4.0 lanes from Ryzen CPU
• (Second PCI-E X16_2 slot is unused)
• PCI-E X1 slot for sound card -- 1 PCI-E 4.0 lane from X570 motherboard chipset
• Bottom M.2 slot for Linux SSD -- 4 PCI-E 4.0 lanes from X570 motherboard chipset
• Third PCI-E X16_3 slot for network card -- 4 PCI-E 4.0 lanes from X570 motherboard chipset
  (i have changed a small bit in setup, instead of network card in x1 slot now it's a sound card.)
  i see,
  so i have to go with above setup in order to keep my GPU slot from splitting in x8 + x8.
  
  Thank you very much, this solves everything.

Notice, however, that the M.2 and 10G NIC are more likely to be limited by the connection between those slots and the chipsets, or the x4 total bandwidth limit between CPU and chipset, than the GPU running at PCIe 4.0 x8.

[Orian Pax]

On 12/15/2020 at 5:16 PM, SpaceGhostC2C said:

Notice, however, that the M.2 and 10G NIC are more likely to be limited by the connection between those slots and the chipsets, or the x4 total bandwidth limit between CPU and chipset, than the GPU running at PCIe 4.0 x8.

okay okay. one more time okay.
I guess I can't have everything I want in technology just yet (atleast on consumer level).

(i guess i will put linux mint on 2.5 inch SSD and let that 2nd NVMe be NTFS storage for windows,
that also means i can buy that 2nd NVMe later).

Rant - Also why people don't make videos on this topic heck even buildzoid doesn't ramble much about this.

as always thanks for help. (that was really informative).

[Jonotallica]

On 12/15/2020 at 7:37 AM, -rascal- said:

 

The Ryzen CPU provides 20 PCI-E 4.0 lanes (16 + 4).

The 16 PCI-E lanes for graphics card is connected to PCI-E X16 slot #1 and #2.

The remaining 4 PCI-E lanes is DEDICATED for the top M.2 slot (M2_1)

The other M.2 slots (e.g. M2_2) gets its 4 PCI-E 4.0 lanes from the X570 chipset.

PCI-E X1 slots are also from the X570 chipset.

 

With your set-up (in the order as you see it physically on the board, top to bottom)

• Top M.2 slot for NVMe SSD -- 4 PCI-E 4.0 lanes from Ryzen CPU
• Top PCI-E X16_1 slot for your GPU -- 16 PCI-E 4.0 lanes from Ryzen CPU
• (Second PCI-E X16_2 slot is unused)
• PCI-E X1 slot for your network card -- 1 PCI-E 4.0 lane from X570 motherboard chipset
• Bottom M.2 slot for your Linux SSD -- 4 PCI-E 4.0 lanes from X570 motherboard chipset
• Third PCI-E X16_3 slot for network card -- 4 PCI-E 4.0 lanes from X570 motherboard chipset

 

PCI-E X16_1 and PCI-E X16_2 slots share the 16 PCI-E lanes from the Ryzen CPU.

If you put your network card into the second slot, the 16 lanes are split into 8 + 8.

 

 

This was very helpful.  One question though about the 4x slot..

 

If you want to run a PCIE4.0 GPU in the top 16x slot, and leave the other (second slot) blank.  The third bottom slot, will be 4x and won't affect the other two?  In other words, it's possible to run..

 

------------------ 16x GPU

 

----------------- empty

-----1x Sound card

----------------- 4x  Capture card or network card (through chipset)

 

I assume this is possible, apologies if this has been answered.  Just wanted to clarify, I'm half asleep typing this.  Also, does the motherboard give the option to choose Gen 4, Gen 3 and Gen 2 for this slot (independantly), while the GPU is plugged into the 16x slot?

[Orian Pax]

15 hours ago, Jonotallica said:

If you want to run a PCIE4.0 GPU in the top 16x slot, and leave the other (second slot) blank.  The third bottom slot, will be 4x and won't affect the other two?  In other words, it's possible to run..

 

------------------ 16x GPU

 

----------------- empty

-----1x Sound card

----------------- 4x  Capture card or network card (through chipset)

Yes it's possible that way.

But first here's the manual link -

https://dlcdnets.asus.com/pub/ASUS/mb/SocketAM4/ROG_CROSSHAIR_VIII_DARK_HERO/E17453_ROG_CROSSHAIR_VIII_DARK_HERO_UM_V2_WEB.pdf

 

secondly yes with the config u said there,

it's possible and works like a charm.

 

But now the problem/query is shifted to will either of the second M.2 or 10 gig networking card get bottlenecked bcuz of shared PCIe lanes between them? If yes then how much?

(And then there are only 4 PCIe lanes in between chipset and CPU, that doesn't help at all.)

 

15 hours ago, Jonotallica said:

Also, does the motherboard give the option to choose Gen 4, Gen 3 and Gen 2 for this slot (independantly), while the GPU is plugged into the 16x slot?

Does this mobo give an option to change manually between 4.0 to 3.0 and 3.0 to 4.0 (considering that PCIe is 4.0)?

Yes it does. Not only this one but others too give this option.

 

Check out the below link

https://amp.reddit.com/r/Amd/comments/cut59x/change_from_autopcie_40_to_30/

 

 

 

_________________________________

 

I will just leave it here. (A line from meme)

 

You CAN use a PCIE 4.0 device (like a graphics card) in a PCIE 3.0 slot and it will work just fine, it’s just that it will run at PCIE 3.0 speeds. Since the very fastest GPU’s (2080 TI) run just a little faster on PCIE 3.0 x16 than on PCIE 3.0 x8, we’ve JUST gotten to the point where the speed difference between PCIE 2.0 and PCIE 3.0 matters for the very fastest cards in a few certain games and situations.

This means it should be another 2–3 years before the difference between a PCIE 3.0 x16 and a PCIE 4.0 x16 matters for the fastest graphics cards and another few years beyond that before it matters for mid-level cards.

So, it’s not that important for several more years, but if you want a PCIE 4.0 motherboard anyway, you shouldn’t need to worry about compatibility, PCIE 3.0 devices should work just fine with your system (and FWIW even PCIE 2.0 too).

 

 

And always thanks for replying.