fix: skip uncorrectable RAPL counter wraps - #1321
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When `max_energy_range_uj` is unreadable, `max_energy_reading` is 0, so the wrap-around branch still ran but corrected nothing, emitting a large negative energy delta straight into the CPU and total energy. Drop the sample instead, matching the EMI backend's behaviour. The same guard also covers driver resets and the transient read-error fallback. A failed read previously returned `Energy(0)`, which looked like a wrap-around and, with a readable `max_energy_range_uj`, injected a spurious positive delta of up to one counter range. `_get_value` now returns None, and the sample is skipped and re-baselined. The uncorrectable-wrap warning is emitted once per file instead of on every measurement cycle. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Closes #1309
What changed
RAPLFile.delta()now re-checks the wrap correction: if the corrected reading is still below the previous one, the sample is dropped (zero energy delta, zero power) with a warning, instead of emitting a negative energy delta.Why
max_energy_range_ujis set to0whenever it cannot be read (codecarbon/core/rapl.py:45). The comment claims wrap detection is then disabled, but only the correction was disabled — the wrap branch still ran and producedenergy_delta = energy - last_energy, a large negative value (up to -1.19e-3 kWh for a 2^32 uJ package domain). That flows unchecked into_total_energy/_total_cpu_energy, and theabs()inPower.from_energies_and_delaymasks it in the power column.The same guard also covers the other sources of a backwards counter: driver resets, suspend/resume, and the
_get_value()transient-error fallback that returns0. It mirrors whatcodecarbon/core/windows_emi.py:566-574already does for EMI.Dropping a sample loses at most one interval of genuine energy — strictly better than subtracting an hour's worth. Systems where
max_energy_range_ujis readable are unaffected.Verification
tests/test_rapl_permissions.py:test_rapl_wraparound_without_max_skips_sample— fails on master (energy_delta.kWhis about -1.11e-3), passes here.test_rapl_wraparound_with_max_is_corrected— pins the existing wrap correction against regression.uv run pytest tests/test_rapl_permissions.py -q→ 2 passed, 2 skipped (the pre-existing Linux-only cases).black --checkclean;ruffreports only pre-existing findings in the touched files.Merge order
This should land before the
rapl_include_dramchange: DRAM domains have smaller max ranges and wrap far more often, which makes this defect fire much more frequently.🤖 Generated with Claude Code