Sharing CPUs via Endpoint Congestion Control

Software network processing relies on dedicated cores and hardware isolation to ensure appropriate throughput guarantees. Such isolation comes at the expense of low utilization in the average case, and severely restricts the number of network processing functions one can execute on a host. In this paper we propose that multiple processing functions should simply share a CPU core, turning the CPU into a special type of "link". We use multiple NIC receive queues and the FastClick suite to test the feasibility of this approach. We find that, as expected, per core throughput decreases when more processes are contending; however the decrease is not dramatic: around 10% drop with 10 processes, and 50% in the worst case where the processing is very cheap (bridging). We also find that the processor is not shared fairly when the different functions have different per packet costs. Finally, we implement and test in simulation a solution that enables efficient CPU sharing by sending congestion signals proportional to per-packet cost for each flow. This enables endpoint congestion control (e.g. TCP) to react appropriately and share the CPU fairly.