Improving the accuracy of software-based clock synchronization and encountering interrupt coalescence

Employing software timestamps is an effective solution for clock synchronization for networks which are already well established, and cannot be replaced at once by devices supporting hardware timestamps. The synchronization performance, on the other hand, with software timestamps is very low when compared with hardware timestamping-based solutions. This work proposes a novel approach to improve the performance of synchronization with software timestamps by enhancing the networking devices with low-cost external timestampers which can accurately timestamp interrupt signals marking the arrival or departure of a packet. The initial experimental results indicate that this approach considerably improves the end-to-end synchronization performance, and it is possible to bring synchronization accuracy from microsecond to nanosecond range. However, timestamping the interrupt signal does not give the correct egress or ingress timestamp for network cards which employ interrupt coalescence. To this end, this work provides experimental results presenting the impact of interrupt coalescent on synchronization.