siddharthrai/pcie-model

A PCIe model

This repository contains a model of PCI Express (PCIe). It allows users to calculate PCIe bandwidth for different hardware configurations e.g., PCIe generation, number of lanes, and negotiated parameters, such as Maximum Payload Size (MPS), Maximum Read Request Size (MRRS), etc.

The code in this repository also allows to model device/driver interactions. This is typically done by adding up how many bytes are transferred to and from the host for a given transaction (or batch of transactions). For example, for a very simple NIC to transmit a packet from the host, the device driver would perform a PCIe write to update the queue pointer. The device would then DMA the TX descriptor and the packet from the host. After the transmission the device would generate a MSI and device driver would read the TX queue pointer. For the receive path similar transactions would occur. The file simple_nic.py contains code to calculate the achievable bandwidth by such a simple NIC.

More realistic/modern devices typically batch some transactions, for example, they DMA groups of descriptors. The file niantic.py contains a model for such a device, a Intel 10Gb/s NIC, code-named Niantic.

Sample code

There are two sample program in the top-level directory (with associated gnuplot files).

• pcie_bw.py prints out the bandwidth achievable at the TLP layer for a given PCIe configuration. It also generates bandwith data for Memory Read (MRd) and Memory Write (MWr) pcie transactions for different payload sizes. This uses the mem_bw.py model.

• nic_bw.py calculates the theoretically achievable bandwidth for a simple NIC and Intel Niantic style NIC using the models mentioned above.

More information

For more information see our SIGCOMM 2018 paper "Understanding PCIe Performance for End Host Networking".

TODO: Add link once available.