Jason Wang wrote: > 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 >
Yes, I will look into it :)
