Ideal ring-to-switch-reduction endpoint-byte ratio
2(n−1)/n; approaches 2 as ranks increasederived
| Value kind | derived — Derived values are guide calculations; their result is only as fixed as the stated inputs, scope, and method. |
|---|---|
| Scope | Ideal bytes only, not measured bandwidth or job acceleration; launch, contention, offload eligibility and fallback still determine completion. |
| As of | 2026-09 |
| Source | NCCL-tests PERFORMANCE.md on GitHub: ring bus-bandwidth normalization. Guide derivation of the ideal endpoint-byte comparison. |
| Derivation | For n ranks of S bytes, ring total sent from endpoints is 2(n−1)S, ideal switch reduction nS; ratio=2(n−1)/n. Counts per direction at endpoint-facing links, excluding headers and internal tree links. |
| Review | checking…review by 2026-11-23 · standard cadence |
| Recorded changes | last 2026-09-16 · 2 revisions tracked |
| Claim id | effective-all-reduce-bandwidth-from-in-network |
Where the guide uses it
← Full numbers register — every date-stamped figure in the guide, with revision history.