Salvatore Del Popolo, University of Trento
Luca Abeni, University of Trento

In general-purpose operating system kernels, the performance of applications that receive and send network packets can be affected by other applications using the network.This is due to the fact that the networking stack processes all the packets in softirq context, regardless of the process or thread which is going to receive them. Hence, a high-bitrate flow of packets destinated to a non real-time process can delay packets destinated to real-time process (or even force the kernel to drop some important "real-time packets").

Early demultiplexing has been proposed in the past as a technique to solve similar problems, by moving packet processing to the receiving task's context. In this way, the network QoS can be controlled by modifying the scheduling parameters of the receiving task (as an additional result, the time spent in processing incoming network packets is correctly accounted to the receiving application, instead of the network softirq).

This paper presents an implementation of early demultiplexing on a modern Linux kernel, showing how this technique allows to increase the predictability of processes which are receiving network traffic. The presented implementation is not intrusive: network device drivers don't need to be modified, no kernel threads are required and code modifications are limited.