Could use some help. How can a lock-free multi-producer ring buffer avoid a Total Store Ordering (TSO) violation on a multi-socket Ice Lake system if a speculative MOVNTDQ (Non-Temporal Store) bypasses the L1-D cache and hits the Fill Buffer during a concu

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Chud 04/08/26 (Wed) 19:39:39 №29794 [Quote]

Could use some help. How can a lock-free multi-producer ring buffer avoid a Total Store Ordering (TSO) violation on a multi-socket Ice Lake system if a speculative MOVNTDQ (Non-Temporal Store) bypasses the L1-D cache and hits the Fill Buffer during a concurrent UPI (Ultra Path Interconnect) snoop-invalidate cycle? Specifically, if the remote socket holds the cache line in the Forward (F) state and the Invalidation Queue on the receiving NUMA node is saturated, what prevents the Store-to-Load Forwarding logic from retiredly committing a stale pointer to the local pipeline before the global RFO (Request For Ownership) has been acknowledged, and can this be mitigated using a LOCK-prefixed instruction without forcing a full serializing CPUID stall that would violate a strict 100ns deterministic latency requirement? Thanks.

Chud 04/08/26 (Wed) 20:01:19 №29796 [Quote]

>>29794 (OP)
ask chatJeetPT

Chud 04/08/26 (Wed) 20:38:51 №29797 [Quote]

Total Store Ordering is guaranteed by the cpu, and cannot be violated by user code, including on Intel Ice Lake.

Chud 04/08/26 (Wed) 20:45:16 №29798 [Quote]

STLF won't forward a stale value locally during a snoop because the FB's valid bits are atomically cleared by the snoop logic. The TSO violation occurs because MOVNTDQ is weakly ordered and allows subsequent normal stores to globally bypass it. While a LOCK prefix architecturally fixes this without serializing the CPU, its reliance on a UPI RFO makes it incompatible with a strict 100ns constraint under your specific F-state/IQ-saturation conditions. SFENCE is the exact instruction designed for this, providing sub-10ns local L3 drain latency without crossing the UPI.