Recovering which physical CPU cores a vendor fused off each individual processor die, from the out-of-band sensor telemetry supercomputers already collect. Reproducible results for 1,962 POWER9 sockets of CINECA's Marconi100.
This project publishes its open issues rather than burying them. The full register — sixteen
entries, each with what is known, what would settle it, and where to look — is
LIMITATIONS.md in
the repository.
Every number comes from one machine, Marconi100. Whether the lot structure or the clustering generalises to other POWER9 installations, or to other vendors, is untested. A replication on a second AC922 installation is the single highest-value addition anyone could make to this work, and it would also settle the defect-versus-policy question below.
If you have per-core BMC telemetry from any comparable fleet, we would like to hear from you — including if your results disagree. A disagreement would delimit exactly when the technique works, which is worth as much as a confirmation.
Slice 0 is harvested on 88.2% of one lot’s sockets but 39.3% of the other’s. Two hypotheses: harvesting follows killer defects, or slice 0 abuts a shared structure and is preferentially fused for reasons of binning policy.
The fitted model cannot separate them, and we no longer claim it can. A correlated defect process and a binning policy that fuses contiguous blocks both predict the clustering we measure. An earlier draft said the decomposition showed “both”; that overstated the identification and was withdrawn.
Posterior-predictive checks add a further constraint: the model is misspecified. It reproduces the distinct-pattern count but not the pattern frequencies, and it misplaces adjacency across the die — over-predicting co-harvest at some slice pairs and under-predicting at others, up to 4.8σ. Whatever drives the clustering is not position-independent.
An earlier version reported a small correlation and concluded that harvest maps are “operationally invisible”. That does not survive two corrections: “no effect” was argued from a small r rather than an equivalence test against a stated margin, and the interval treated node-days within a rack as independent.
Re-run over the full record with covariate adjustment and rack-clustered intervals, only one of three map features is bounded below a ±5 W margin. The strongest moves socket power +7.9 W across its range, 90% CI [+0.9, +16.6]. The honest summary is bounded, not negligible.
We record this because it is the most transferable thing we learned: analysis choices moved our numbers more often than the data did, four times, and every one of them ran in the direction we would have preferred.
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