mesh-meter: a span shorter than its counter's minimum window is an estimate #630

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dcharlot merged 1 commit from mesh-meter/min-window into main 2026-11-05 04:31:21 -05:00

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2026-11-04

Transaction Science

mesh-meter: a span shorter than its counter's minimum window is an estimate ...

A counter declares the smallest window over which its readings are not noise
(min_window_ns: about 10 ms for RAPL and IOReport, 100 ms for NVML; 2 s for a
Mac's SMC power integral). Across a shorter span its delta is whatever its
updates and quantization gave, often zero or a whole update period, yet mesh
graded it at the counter's grade: a few-millisecond request could be sealed
HwShunt at 0 µJ, or ModelBased at a power reading's extrapolation.

- SPEC 3.3: a span shorter than the minimum window of the counter that would
  grade it MUST NOT be graded HwShunt or ModelBased from that counter; it is
  an estimate of the request, and SHOULD be billed by an estimator that
  resolves the span's own length, so a short request is never billed zero.
- HwMeter opens its own window (Meter::open_span), which Session uses: it
  times the span, and one shorter than the backend's floor
  (HwMeter::min_window) is billed this crate's EstimatorMeter over the span's
  own length, graded Estimator with no measured_uj, as a span across a failed
  read is. Past the floor the counter's figure stands, graded as before.
  min_window is zero where the bridge already bills by its estimator.
- ProcessMeter: where ProcessSpanMeter falls back to the host meter, a span
  shorter than the host meter's floor is billed the same way. Spans its own
  CPU and GPU counters metered are not the host meter's and are unaffected.
- jouleclaw-energy: ProcessSpanMeter::fallback_min_window, the active fallback
  meter's min_window_ns, so a caller can apply the rule. Additive.

Each span is timed from after its opening read to before its closing one, a
little shorter than the counter's own window, so a span at the floor is judged
short rather than long.

Tests: under a 50 ms floor a 20 ms span is Estimator at the estimator's figure
for 20 ms, and a 60 ms span keeps the counter's figure and grade (HwShunt and
ModelBased); the bridge's minimum window is its counter's until a failed read,
then zero; a host-meter fallback span under the host floor is an estimate,
past it the host figure stands, and a span this process's own counters
metered keeps its grade. Linux x86_64: mesh-meter (default, hw-meter-rapl),
mesh-core (hw-meter-rapl) and mesh-conformance pass; clippy clean. macOS
(M3 Ultra): mesh-meter and mesh-core with hw-meter-apple pass, including a
real in-process serve sealed HwShunt; clippy clean for mesh-meter and
jouleclaw-energy.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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