ping? On 28/09/2026 16:24, David Vrabel wrote:
When a VM has been assigned a number of PCIe devices behind a common PCIe switch and the VM intends to use peer-to-peer (P2P) transfers between the devices, it is useful to be able to more report the apparent PCIe bandwidth so it reflects the real handwidth of the underlying hardware. This allows software in the VM (such as NCCL[1]) to make better decisions about whether to use P2P or not. The existing emulated PCIe switch is a vintage TI XIO3130 and only support 2.5 GT/s and x1, so we introduces new generic upstream and downstream port devices (pcie-upstream-port and pcie-downstream-port), inspired by the existing generic pcie-root-port device. The existing experimental "x-speed" and "x-width" options are made non-experimental, allowing the pcie-root-port and pcie-downstream-port capabilities to be configured to match the hardware. The pcie-root-port device is updated to default to a Gen6 capable device. Finally, where a root or upstream port's bandwidth has been limited, we also ensure the other end of the link reports the same link status.
