xdp-project-bpf-examples/pping/TODO.md

TODO

Protocols

• TCP (based on timestamp options)
  • Skip pure ACKs for egress
    • Timestamping pure ACKs may lead to erroneous RTTs (ex. delay between application attempting to send data being recognized as an RTT)
  • Add fallback to SEQ/ACK in case of no timestamp?
    • Some machines may not use TCP timestamps (either not supported at all, or disabled as in ex. Windows 10)
    • If one only considers SEQ/ACK (and don't check for SACK options), could result in ex. delay from retransmission being included in RTT
• ICMP (ex Echo/Reply)
• QUIC (based on spinbit)

General pping

• Add sampling so that RTT is not calculated for every packet (with unique value) for large flows
  • This serves two purposes, limiting the output from pping and reducing the rate at which the timestamp map grows (making it less likely to become full)
  • Will likely be based on a per-flow rate limit
• Keep some per-flow state
  • Will likely be needed for the sampling
  • Could potentially include keeping track of average RTT, which may be useful for some decisions (ex. how often to sample, when entry can be removed etc)
  • Could potentially include keeping track of minimum RTT (as done by the original pping), ex. to track bufferbloat
  • Could potentially include keeping track of if flow is bi-directional
    • Original pping checks if flow is bi-directional before adding timestamps, but this could miss shorter flows
• Improve map cleaning: Use a dynamic time to live for map entries based on flow's RTT, instead of static 10s limit
  • Keeping entries around for a long time allows the map to grow unnecessarily large, which slows down the cleaning and may block new entries
• Add support for automatically deleting entries if they are unique
  • TCP timestamp need to be kept for a while so only first packet with unique value is timestamped. For identifiers that are unique per packet, they can be removed directly after RTT is calculated
  • Once sampling is introduced, keeping entry around will not be sufficient to guarantee only timestamping first packet. May at that point remove every entry once RTT is calculated.
• Use libxdp to load XDP program
• Add option for machine-readable output (as original pping)
• Add timestamps to output (as original pping)
• Add support for other hooks
  • Ex TC-BFP on ingress instead of XDP?

Done

• Clean up commits and add signed-off-by tags
• Add SPDX-license-identifier tags
• Format C-code in kernel style
• Use existing functionality to reuse maps by using BTF-defined maps
  • Use BTF-defined maps for TC-BPF as well if iproute has libbpf support
• Cleanup: Unload TC-BPF at program shutdown, and unpin map - In userspace part
• Add IPv6 support
• Refactor to support easy addition of other protocols