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b2c9e9bd71
For large tailnets (~50k+ nodes) with frequent peer churn (ephemeral
GitHub Actions workers etc.), tailscaled used to rebuild the full
netmap and fan it out on the IPN bus on every MapResponse that
added or removed a peer. Two compounding O(N) costs per delta: the
full netmap rebuild + every Notify.NetMap encode to every bus watcher.
This change tackles both:
1. Plumb O(1) peer add/remove through the delta path. PeersChanged
and PeersRemoved no longer veto the delta path; instead they
mutate the per-node-backend peer map in place.
2. Restrict ipn.Notify.NetMap emission to the platforms whose host
GUIs still depend on it (Windows, macOS, iOS) and migrate
in-tree consumers off it everywhere else:
- Migrate reactive consumers (containerboot, kube agents,
sniproxy, tsconsensus, etc.) off Notify.NetMap to the
previously-added Notify.SelfChange signal so they no longer
have to subscribe to the full netmap.
- Add ipn.NotifyNoNetMap so GUI clients on legacy-emit platforms
that have already migrated can opt out of the per-watcher
NetMap encode.
- Gate Notify.NetMap emission on the producer side by a compile-
time GOOS check, so the supporting code is dead-code-eliminated
on Linux and other geese where no GUI consumer needs it.
Re-running BenchmarkGiantTailnet from tstest/largetailnet, which was
added along with baseline numbers on unmodified main in ad5436af0d57,
the per-delta cost (one peer add+remove pair) is now ~O(1) regardless
of tailnet size N:
N no-watcher (ms/op) bus-watcher (ms/op)
before now factor before now factor
10000 32 0.11 300x 166 0.13 1300x
50000 222 0.11 2000x 865 0.13 6700x
100000 504 0.12 4100x 1765 0.13 13400x
250000 1551 0.12 12500x 4696 0.15 32400x
Updates #12542
Change-Id: I94e34b37331d1a8ec74c299deffadf4d061fda9e
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>