Commits on Sep 25, 2024

1. feat: deliver UDP packets from same connection in receiving order …

   All UDP packets are queued into a single channel, and multiple
   workers are launched to poll the channel in current design.
   
   This introduces a problem where UDP packets from a single connection
   are delivered to different workers, thus forwarded in a random order
   if workers are on different CPU cores. Though UDP peers normally
   have their own logic to handle out-of-order packets, this behavior will
   inevitably cause significant variance in delay and harm connection quality.
   Furthermore, this out-of-order behavior is noticeable even if the underlying
   transport could provide guaranteed orderly delivery -  this is unacceptable.
   
   This commit takes the idea of RSS in terms of NICs: it creates a distinct
   queue for each worker, hashes incoming packets, and distribute the packet
   to a worker by hash result. The tuple (SrcIP, SrcPort, DstIP, DstPort, Proto)
   is used for hashing (Proto is always UDP so it's dropped from final
   implementation), thus packets from the same connection can be sent to
   the same worker, keeping the receiving order. Different connections can be
   hashed to different workers to maintain performance.
   
   Performance for single UDP connection is not affected, as there is already
   a lock in natTable that prevents multiple packets being processed in different
   workers, limiting single connection forwarding performance to 1 worker.
   The only performance penalty is the hashing code, which should be neglectable
   given the footprint of en/decryption work.

   

   updateing committed Sep 25, 2024
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