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How can I change by software the bandwidth of a PCIe GPU from 16x to 8x ? I use an Asus Hero XI and Windows 10 Enterprise, and a 2080ti.

I could not find anything in the BIOS or in Windows GP or drivers or anything.

Soleil
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    Why is it exactly that you're wanting to limit the number of PCIe lanes your GPU uses? I feel like this could be an XY problem. – Sam Forbis Feb 14 '20 at 14:36
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    It's about benchmarking memory bound processes. – Soleil Feb 14 '20 at 15:18
  • I see. That's certainly a valid reason for wanting to limit PCIe lanes. Thanks for the info! – Sam Forbis Feb 14 '20 at 15:19
  • I don't think this is possible with software. I don't even think there's an option for it in the BIOS. You'd have to physically move the card to an 8x slot or physically disconnect the upper 8 lanes – Sam Forbis Feb 14 '20 at 15:22
  • I have an option to change pcie 4x to 2x for nvme drives (and subsequently have 4->6 sata ports) – Soleil Feb 14 '20 at 15:26
  • That option is likely only there for the specific reason you just stated - so you can use more SATA ports. Lowering the number of lanes that go to an actual slot is almost never necessary and has no impact on other portions of the system other than other PCIe cards, and therefore doesn't have a software setting that can change it. As batistuta stated, placing another device in the second PCIe slot should reduce slot 1 to 8x. – Sam Forbis Feb 14 '20 at 15:29
  • @SamForbis I actually can change the generation (gen1/2/3). So: is pcie 16x gen2 really equivalent to pcie 8x gen3 ? – Soleil Feb 14 '20 at 15:33
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    It should give you approximately the correct results if you go from Gen3 to Gen2. – Sam Forbis Feb 14 '20 at 15:35
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    @Soleil - Are two versions of the PCIe specification equivalent to one another. No; They are not equivalent. Those firmware options basically enable/disable hardware features. – Ramhound Feb 14 '20 at 17:24
  • Here https://unix.stackexchange.com/questions/42361/force-re-negotiation-of-pcie-speed-on-linux I see that the energy state can slow down the pcie speed. Can I force the energy state to bet at a certain level so it is equivalent to a x8 speed ? – Soleil Feb 14 '20 at 21:58

2 Answers2

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You cannot change it manualy. But slot1 will switch to 8x, if you put any device in slot2

batistuta09
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I dont know of any software that will allow you to limit PCIe bandwith.

Looking at the ASUS Hero XI manual, it seems the only way to limit it there is to switch back to Gen2. As stated above already, it should negotiate Gen2 speeds halving your bandwith.

Third option would be to block of half of the pins on the gfx cards.

Silbee
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