rebbarb

T

Roflin 8691b09676 docs: record netboot throughput at 6.4 s and what txto=0 does and does not say

300908 bytes in 6.4 s (0.38 Mbit/s) with txto=0, down from 40.1 s and 16.9 s.
The whole cost was round-trip, not bandwidth: stop-and-wait is one block per
round trip.

The counter-intuitive result is recorded deliberately: raising the host timeout
0.1 -> 0.3 barely changed the retry count (110 -> 95) but tripled the cost of
each, making the transfer 2.4x SLOWER.  Short is correct here because the GC
re-ACKs a duplicate immediately, so a premature retry costs one timeout and
nothing else.  Anyone tuning this later will reach for a longer timeout first;
the note says not to.

Also corrects my own earlier claim.  I concluded from the 0.3 s result that the
misses were LOST ACKs rather than late ones.  txto=0 shows every ACK reached
the W5100 with TI set, so the drain and EXI side are clean -- but TI is not
proof of transmission, and a 6.4 s total is hard to reconcile with ~95 genuine
losses.  The honest state is that it is not established either way, and the
retry COUNT at 0.05 s is the measurement that would settle it.  Recorded as
open rather than fixed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

2026-10-09 19:56:13 +02:00