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 mmap vs buffered read lab: 256 MiB p50 11.5 vs 5.4 GB/s; O_DIRECT ~0.9 GB/s warm-cache bypass. Fake endpoint-only GB/s disclosed. No Docker.
Hands-on nginx gzip on/off lab: HTML ~107x smaller at level 1; JSON RPS ~1987 off vs ~1031 l1 vs ~563 l6 on localhost. Measured numbers, 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.