PCI-E SWITCH ARBITRATION

[agendarsky]

if you have input lag, heavy mouse, broken bhop timing that persists across every platform, every OS, every driver tweak — get an intel NIC and plug it into a PCIe slot that bypasses your FCH/PCH. mine is intel 82580, $15 used server card. here's why it works: your onboard NIC and your USB controller (where your mouse lives) share the same physical PCIe switch deep in the chipset tree. every DMA transfer from the NIC occupies that switch and your mouse interrupt waits. microseconds, but variable, thousands of times per second. that variance is your input lag. doesn't matter if you're playing offline or against bots — realtek is soft-MAC, it's hammering that switch with small DMA bursts constantly even at idle. intel 82580 sits CPU-direct, one hop, never touches the USB switch. 15 years, every platform, same problem. one cheap server card fixed it. before buying anything run lspci -tv and find slots that go through 00:01.x not 00:02.x or deeper. everything else — C-states, HPET, RAM OC, scheduler, GPU tweaks, threadirqs — negligible. fix the topology first. hopefully, on most of modern boards , the second pcie x16 slot should be connected directly to cpu root complex instead of pch/fch, and yes u can connect pcie x1 card into the pcie x16 slot.

[agendarsky]

also forgot to mention — my setup if anyone's wondering: GPU in the primary x16 slot, dedicated Renesas xHCI card in the x1 slot directly above it for mouse and keyboard, intel 82580 in the bottom x16 slot, onboard Realtek disabled in BIOS. Scarlett 4i4 and MIDI keyboard on onboard USB ports. NIC is CPU-direct, completely separate from the USB stack. the Renesas xHCI card shares the same FCH switch as the onboard USB ports where i have the Scarlett and MIDI keyboard — but that's fine, neither of those generates unpredictable DMA traffic. mouse and NIC are on completely different PCIe branches and never contend for the same switch.

[nickchraj]

unfortunatly it happens even when the NIC is disabled on bios so this wont work for me

[SammYrai]

So I could use any Intel Nic even a 226-T1 as long as I plug it into a pcie-slot that is it is on 00:01.x?

[Panychkaaa]

Tried in 2023...
Sorry. Doesn't help.
Long ago: Gigabyte Z390 UD, MSI(390), Asrock(don't remember), ASUS ROG STRIX B650E-F GAMING WIFI, MSI B850 GAMING PLUS WIFI
Acquired yesterday: ROG STRIX B850-A GAMING WIFI
Replacing components helps a little. It's true. But it's very expensive.

[agendarsky]

I know dude I was experimenting with this long time ago, but I've never really was checking number of switches lane pass through, maybe also type of switch matters. On this particual mobo with this nic sitting in root complex , I can just reset bios settings and go default settings and it works flawlessly, also iordered cheap nic with realtek chip on it, I'm interesting if this can be just bad driver implementation

[shebu]

This doesn't explain laaags if there is no network card at all.

[agendarsky]

Potentially any device including xhci controller itself if topology is bad? For me it was always better when all onboard stuff was off.

[Panychkaaa]

Sorry my English bad. I write briefly.
Realtek -> Bad
Intel -> Good
I checked many times.