skeg-telemetry

Zero-overhead atomic counters and histograms for skeg.

Design

• Every public API entry is #[inline(always)].
• All counters and histograms are static AtomicU64 arrays. No HashMap, no Mutex, no allocation on the hot path.
• Per-op counters are sharded across MAX_SHARDS = 32 to avoid false sharing on M-series P-cores.
• Histograms are fixed exponential buckets (1 µs → 1 s, plus +Inf).
• When the crate is compiled with no features, every public function is an empty body and the caller's arguments are sunk into let _ = … — verified with cargo asm to compile to a tail call elimination.

Features

When neither feature is on, this crate is a no-op.

Hot-path cost budget

record_op is gated by benches/overhead.rs:

CI fails if any benchmark drifts past its budget.

Usage

use skeg_telemetry::{record_op, Op};

let t0 = std::time::Instant::now();
do_vsearch();
record_op(Op::VSearch, shard_id, t0.elapsed());

For the HTTP exporter:

skeg_telemetry::http::spawn("127.0.0.1:9090".parse().unwrap())?;

For the RESP3 STATS command body:

let body = skeg_telemetry::stats::dump_text();