Hands-on ctx-switch lab: process pipe RTT p50 3.2 us (~0.50M sw/s); thread pipe 2.85 us; Event 9.3 us; 6 hogs blow p95 to 19 us. Real numbers, no Docker.
Hands-on asyncio vs ThreadPool lab: sleep 58.7× vs 44×; delayed TCP 13.8× vs serial; fast-echo trap loses; CPU flat. Real localhost numbers, no Docker.
Hands-on flock lab: uncontended LOCK_EX p50 0.33 us; waiter ~50 ms hold; w8 p50 ~36 ms; LOCK_NB 99% fail; LOCK_SH ~6.7x wall. Real numbers, no Docker.
Hands-on TLS handshake lab: Python full HS p50 TLS1.3 1.51 ms vs TLS1.2 1.20 ms (~72× TCP); openssl resume ~1.5× / 4.1×. Localhost RSA numbers, no Docker.
Hands-on stdout buffering lab: full buffering maximizes throughput, while line and unbuffered modes restore live visibility on pipes.
Hands-on ProcessPool vs ThreadPool lab: pure-Python threads lose to processes, hashlib threads help, and sleep I/O favors threads.
Hands-on epoll vs select toy: ready-wait flat ~3.5 µs (8→900 FDs); select scales 4.6→16.9 µs then hits fd≥1024 cliff. Python numbers, no Docker.
Hands-on sendfile vs read+sendall lab: 256 MiB p50 4.41 vs 2.34 GB/s (~1.9×); copy collapses at 4 KiB. Warm localhost TCP measured, no Docker.
Hands-on pipe vs tmpfile IPC lab: 5.32 vs 1.51 GB/s bulk (fsync 0.57); 64 B RTT p50 3.3 us vs 70 us vs 289 us. Localhost measured, no Docker.
Hands-on TCP_NODELAY vs Nagle: 1-byte reuse 124k vs 73k RPS; 32×16B writes favor Nagle (~1.7× fewer OutSegs). Delayed-ACK mean trap on localhost.
Hands-on RLIMIT_NOFILE lab: soft=64 → EMFILE after 58 held accepts; soft=512 takes 200/200. Soft raises without root; hard does not. Real numbers.
Hands-on SO_REUSEPORT lab: ss shows 4 listen queues; backlog=8 flood 72% vs 62% OK; ~41% fewer ListenOverflows. Real localhost numbers, no Docker.