• Competitor rules

    Please remember that any mention of competitors, hinting at competitors or offering to provide details of competitors will result in an account suspension. The full rules can be found under the 'Terms and Rules' link in the bottom right corner of your screen. Just don't mention competitors in any way, shape or form and you'll be OK.

Help with PCIe question - 7900XT reported at PCIe 4.0 @ x4

Havana_UK

Havana_UK

Havana_UK

Soldato
Joined
14 Oct 2004
Posts
5,310
Location
location, location
After a bit of help...

I'm out of touch with the latest hardware these days, but recently upgraded my machine with an i5 12600K + Mobo & RAM from MM, and a new 7900XT.

All the benchmarks and gaming suggest it's performing pretty much as expected, however both GPU-Z & AMD Adrenaline report the card as always running at PCIe 4.0 @ x4 when, my understanding, is that it should be running at x16. It doesn't change the reported values when either gaming or benching.
- 3D Mark Timespy score is 23,165 (Graphics score 26,126)

Complete specs are:
- i5 12600K @ 5.1GHz P core, 3.9 GHz E core
- MSI PRO Z690-A DDR4
- 32GB Patriot DDR4 3600 C18
- Sapphire Pulse 7900XT @ stock
- NVMe drives: WD SN850X in slot 1, WD SN770 in slot 4 (I also tried it in slot 2)

I mention the NVMe drives as I know they connect directly to the CPU's PCIe lanes, which are limited (I think 24 lanes on Alderlake?)

I've tried removing the second NVMe drive, but this doesn't change anything in terms of how the card reports.

I've tried reseating the card multiple times without any change, and I've also done a completely fresh Win11 install as well.

Any suggestions please?
 
There isn't any lane splitting with nvme for this motherboard. As long as GPU is in first x16 slot it should get full bandwidth.

Not sure if motherboard even supports it, but maybe somehow PCIe lane bifurcation x4/x4/x4/x4 got turned on in bios? Bios reset could fix it?

Or maybe its a power saving feature and it goes to 16x when in game? Although usually PCIe x16 4.0 goes to PCIe x16 1.1 to save power

Have you tried a different GPU?

Lastly, long shot, try reseating the CPU. Maybe by stroke of bad luck some CPU pins responsible for x16 aren't making contact
 
alec said:
There isn't any lane splitting with nvme for this motherboard. As long as GPU is in first x16 slot it should get full bandwidth.

Not sure if motherboard even supports it, but maybe somehow PCIe lane bifurcation x4/x4/x4/x4 got turned on in bios? Bios reset could fix it?

Or maybe its a power saving feature and it goes to 16x when in game? Although usually PCIe x16 4.0 goes to PCIe x16 1.1 to save power

Have you tried a different GPU?

Lastly, long shot, try reseating the CPU. Maybe by stroke of bad luck some CPU pins responsible for x16 aren't making contact
Click to expand...
Thanks Alec, things to check!

<update> I'll check the lane bifurcation first. <there's no lane bifurcation support in this MB as far as I can tell>

I can pinch my son's new 6800 which is running PCIe 4.0 x16 in his PC to also test if the above doesn't help.

Nothing seems to drag it from PCIe 4.0 x4 regardless of stressing the GPU, so I don't think it's anything power saving going on.

If all else fails I'll try reseating the CPU as you suggest.
 
Last edited:
Tetras said:
Was the board uhm, well-used (i.e. dusty)?

Have you done a cmos clear?
Click to expand...
The board was in very good condition, no dust at all.

Just tried my 7900XT in my son's new build (in place of his 6800) and it works fine, immediately reports at PCIe 4.0 x16 in Adrenaline and GPU-Z. Weirdly I got no display output with his GPU in my machine, but I'm not sure if this is because it requires 3 x PCIe power connectors (and I've only got 2x available). Regardless I think this narrows down the source of the problem to my motherboard or CPU though, at least I know the GPU itself is fine.

I've not tried a CMOS clear yet, will do that next.
 
OK, found another PCIe power connector for my PSU and added it...6800 now powers up fine, but in Adrenaline it reports at PCIe 4.0 x4, just like the 7900 XT.

CMOS reset time...
 
eeii said:
Might be worth doing a bios update and checking in the bios for forcing the slot to x16
Click to expand...
Have already updated the latest BIOS, and can't find anything to force x16. I can only choose PCIe 1.1 up to PCIe 5.0 (or Auto), but nothing else.

Have now tried cleaning the PCIe slot but hasn't changed the situation...still stuck on x4. Will try removing and reseating the CPU later to see if that helps.
 
I'm not sure it applies to you but some boards have a setting where you can change the x16 slot to x4 + x4 + x4 + x4 to add four NVME drives.
 
Does moving the SN850X drive in M2_1 slot to M2_2 help at all? I know you mentioned fiddling with the secondary drive but not the first. Just wondering if shifting it from the CPU lanes to the Z690 chipset does something magical for the PCI_E1 slot which is also from CPU.
 
Firegod said:
Does moving the SN850X drive in M2_1 slot to M2_2 help at all? I know you mentioned fiddling with the secondary drive but not the first. Just wondering if shifting it from the CPU lanes to the Z690 chipset does something magical for the PCI_E1 slot which is also from CPU.
Click to expand...
This I've not checked, but is one last thing for me to try.

AthlonXP1800 said:
Did you tried run GPU-Z PCI Express Render Test to see if PCIE 4.0 jumped up to X16 speed?

Is your CPU cooled with Air cooler or AIO cooler?
Click to expand...
Yes, I've tried that and it doesn't have any impact (neither does benchmarking/stressing the GPU, nor gaming on it).

CPU is air cooled with Noctua D15S. It's running nice and cool, idling around 25 degrees and peaks at 80 degrees under full load (i.e. Cinebench), but typical gaming/GPU benching it's not exceeding 65 degrees.

I'm now officially flumoxed. I've reseated (and cleaned + repasted) the CPU & heatsink, I can see no evidence of any dust or contamination of damage to the CPU socket or pins. If moving the boot drive from M2 slot 1 to elsewhere doesn't fix anything then I either have a dodgy CPU or dodgy motherboard I think.
 
Previous owner may used CPU air cooler that could damaged CPU socket or motherboard due to heavy weight pressure.

Or BIOS settings messed up after I read manual stated your motherboard has 3 PCI Express X16 slots so I found someone who had same issue had found solution.

[SOLVED]STRIX z390-E Gaming PCIEX16_1 @x4

Today I flashed to newer BIOS, but to be honest I have no idea if the problem was before or not. Anyway I discovered that my 1080 GTX card is working at X4 speed instead of x16 on PCIEX16_1 port. I have no other PCIE card installed, only two M.2 Disks in mobo slots. No SATA drives. I tried...
rog-forum.asus.com rog-forum.asus.com

If your GPU is installed on PCI E1 slot then try disabled PCI E2 link speed in BIOS and see if it free up PCIE bandwidth by run GPU-Z PCI Express Render Test to see if it run at full speed PCIE 4.0 @ X16. If not then try disabled PCI E3 link speed and try again.
 
AthlonXP1800 said:
Or BIOS settings messed up after I read manual stated your motherboard has 3 PCI Express X16 slots so I found someone who had same issue had found solution.
Click to expand...

Interesting, might be worth asking the previous owner what slots they used too, though I'd have expected the cmos reset to have fixed this.
 
So, the motherboard has 3 PCIe x16 sized slots, but actually only PCIe slot #1 is a x16 slot. The other two are actually x4 slots only. In the BIOS I can only set the speed of slot #1, and there I can basically choose Auto or anything up to PCIe Gen 5.

I've now also tried my last possibility, removing NVMe drive #2, and putting the SN850X in a different slot (one served by the chipset, not the CPU), but it hasn't changed anything. GPU still running at PCIe Gen 4 x4 :(

On the plus side, it really seems to have almost no impact in gaming or benchmarking, but it's frustrating that it's not working as it should. Ho hum...I was considering an i7 14700K for this, but I guess I'll just wait it out a while and maybe move to an AM5 platform later instead.
 
You must log in or register to reply here.
Back
Top Bottom