On Tue, Sep 2, 2025 at 4:10 PM Simon Schippers <simon.schipp...@tu-dortmund.de> wrote: > > This patch series deals with TUN/TAP and vhost_net which drop incoming > SKBs whenever their internal ptr_ring buffer is full. Instead, with this > patch series, the associated netdev queue is stopped before this happens. > This allows the connected qdisc to function correctly as reported by [1] > and improves application-layer performance, see benchmarks. > > This patch series includes TUN, TAP, and vhost_net because they share > logic. Adjusting only one of them would break the others. Therefore, the > patch series is structured as follows: > 1. New ptr_ring_spare helper to check if the ptr_ring has spare capacity > 2. Netdev queue flow control for TUN: Logic for stopping the queue upon > full ptr_ring and waking the queue if ptr_ring has spare capacity > 3. Additions for TAP: Similar logic for waking the queue > 4. Additions for vhost_net: Calling TUN/TAP methods for waking the queue > > Benchmarks ([2] & [3]): > - TUN: TCP throughput over real-world 120ms RTT OpenVPN connection > improved by 36% (117Mbit/s vs 185 Mbit/s) > - TAP: TCP throughput to local qemu VM stays the same (2.2Gbit/s), an > improvement by factor 2 at emulated 120ms RTT (98Mbit/s vs 198Mbit/s) > - TAP+vhost_net: TCP throughput to local qemu VM approx. the same > (23.4Gbit/s vs 23.9Gbit/s), same performance at emulated 120ms RTT > (200Mbit/s) > - TUN/TAP/TAP+vhost_net: Reduction of ptr_ring size to ~10 packets > possible without losing performance > > Possible future work: > - Introduction of Byte Queue Limits as suggested by Stephen Hemminger > - Adaption of the netdev queue flow control for ipvtap & macvtap
Could you please run pktgen on TUN as well to see the difference? Thanks
