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ab9 on the AMD bench: pipe.throughput's per-round writer thread follows spawn placement's rotation over the whole machine, and every round that lands it in the other LLC from its reader reads slow, in both arms and without exception. One unexplained same-LLC slow round is recorded as an open observation. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This was referenced Nov 3, 2026
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Files
issues/a-spawned-thread-starts-in-any-llc-not-its-spawners.md, a defect in spawn placement found by #1129's ab9.Problem
CpuHandles::placebreaks ties by a rotation over the whole machine and never weighs the spawner's LLC. On the AMD bench,pipe.throughput's per-round writer thread followed that rotation (14, 15, 0, … 5 at 16384) in all six ab9 boots of both arms. Every round that put it in the other LLC from its reader read slow, without exception: about 2.0, 3.5 and 4.8 GB/s at 4096, 16384 and 65536, against about 5.0, 8.4 and 10.0 in one LLC. One same-LLC base round read 5.6 GB/s with nothing in its record to explain it; the issue records it as an open observation.Evidence: ab9 judgment, per-boot rows.
Resulting behaviour
None: issues only. The fix (a spawned thread prefers a free core in its spawner's LLC) follows as its own PR, which the issue is assigned to.
Checks
None run: the change is one Markdown file. No gate checks issue frontmatter; review does (
issues/README.md).🤖 Generated with Claude Code