Hello all, I’m wondering if I’m running into a bottleneck with PCIe 4.0 running from the Chipset on x570. I’m running a Windows 10 VM and on my VM, I get speratic sluggish performance in games, especially with I/O updating in games, like when new entities are loading or a new chunk is loading. I’m fairly certain it’s because I’m running the GPU, NIC and USB Card on the Chipset and the NMVe Drive on the CPU. So, with all PCIe devices and the Chipset running at PCIe 4.0 and over x4 lanes, is it really the bottleneck?
MOBO: Asus Prime x570-P
CPU: Ryzen 3700x
Full PC parts list
The setup is as follows:
Host: Manjaro Linux
SSD: Samsung 970 Evo NVMe 1TB on Chipset M.2_2
GPU: Nvidia 980 PCIe16x_1
NIC: on-board Realtek GB
All devices are passed through to VM.
VM: Windows 10
SSD: Samsung 970 Evo NVMe 1TB on CPU M.2_1
GPU: Nivdia 1080 on PCIex16_2 running at 4x 4.0, on chipset
RAM: 16GB (Half of Host RAM)
NIC: Broadcom 1 GB NIC PCIe 1x
USB Host Card on PCIe 1x
The 1080 is a pci 3.0 card, so you’re not running it at 4.0 despite the feature being supported by your motherboard.
Since the latency is intermittent I’d look at other things your host OS might be doing. Run the
glances app or something else like
htop on the host in a window from your guest, and see if you can recreate the lag, watching for something to get flagged.
I’m guessing you can’t swap your GPU slots to determine if bandwidth is an issue? (Although I doubt it is since PCIe 4.0 x4 ~= PCIe 3.0 x8, which is plenty for GPUs
I get that the 1080 will run at 3.0 speed, but the Chipset 4x up-link to the CPU is set to run at 4.0, that in theory should give me 8x speed.
Yeah, I can’t swap slots as the BIOS doesn’t have an option to select the Boot GPU slot. I tried to have Xorg select the boot gpu, but this didn’t work because the BIOS is blocking it. From what I’ve read, only Gigabyte allows this option. I’m looking at upgrading to Asus PRIME x570-PRIME which the top two PCIEx16 slots are connected to the CPU at 8x in dual mode.
PCI 3.0 at x4 throughput is roughtly 3900MB/S, as @gordonthree mentioned gtx 1080 is PCI 3.0 and lesser. For this configuration 8x transfer rate would be minimum Maybe an issue unreported and could you some investigating and patched via software or an AMD agesa update (especially on the x570 platform). I have a 990fxa gigabyte board and the gpu boot option is great and always a welcome mainstay within the brand. (Asus is hit or miss in this regard and may only support this feature on their WS [workstation] line of motherboards)
Thank you all for the replies, but I think the point being missed here is that the 1080 is in the second PCEx16 Slot and running at x4 which IS NOT RUNNING THOURGH TO THE CPU, but to the chipset! The chipset is running at 4x, @ 4.0 speeds to the CPU, so only x4 lanes are going to the CPU. I think the bottleneck is the fact that I have not only the 1080 running on the 4x lanes from the chipset to the CPU, but also the NMVe drive, the 1GB NIC and the USB PCie host card. All these devices look to be fighting for a path to the CPU to be processed. This I believe is the core issue.
Is a 100MBit jack connected to a 10GBit switch faster too?
On the other hand, a B550 chipset is routed all through the chipset
Integrated in the CPU (PCIEX16/PCIEX8):
3rd Generation AMD Ryzen processors:
1 x PCI Express x16 slot, supporting PCIe 4.0 and running at x16 (PCIEX16)
1 x PCI Express x16 slot, supporting PCIe 4.0 and running at x8 (PCIEX8)
2nd Generation AMD Ryzen processors:
1 x PCI Express x16 slot, supporting PCIe 3.0 and running at x16 (PCIEX16)
1 x PCI Express x16 slot, supporting PCIe 3.0 and running at x8 (PCIEX8)
- For optimum performance, if only one PCI Express graphics card is to be installed, be sure to install it in the PCIEX16 slot.
- The PCIEX8 slot shares bandwidth with the PCIEX16 slot. When using the 3rd Generation AMD Ryzen processors / 2nd Generation AMD Ryzen processors, the PCIEX16 slot operates at up to x8 mode.
2nd Generation AMD Ryzen with Radeon Vega Graphics processors / AMD Ryzen with Radeon Vega Graphics processors:
1 x PCI Express x16 slot, supporting PCIe 3.0 and running at x8 (PCIEX16)
Integrated in the Chipset (PCIEX4/PCIEX1):
1 x PCI Express x16 slot, supporting PCIe 4.0*/3.0 and running at x4 (PCIEX4)
- For 3rd Generation AMD Ryzen processors only.
Future configurations to try out: 10Gbit x4 upgrade later, x4 capture card for home video camera.
Thank you for the reply, I understood the issue and the point you were making. And that’s the board I’m looking at to replace the Asus x570-p, but my flatmate has an extra Asus PRIME x570-Pro https://www.newegg.com/asus-prime-x570-pro/p/N82E16813119196, which the top two PCIEx16 slots are connected to the CPU at 8x in dual mode. I might try the Prime first to see if it indeed does fix the issue as I believe it will.
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