Per feedback_gpu_cpu_roundtrip.md, the per-seed dtoh in
launch_thompson_direction (10k iterations for Test 0.A, 100k for Test
0.B) violated the no-dtoh-on-hot-or-tight-loop invariant. Replaces
the per-seed kernel with a batched kernel (one thread per seed) and
the dtoh wrapper with a MappedI32Buffer using cuMemHostAlloc(
DEVICEMAP|PORTABLE) — same pattern as gpu_training_guard.rs
MappedBuffer.
Kernel changes (thompson_test_kernel.cu):
- thompson_direction_test_batched: replaces thompson_direction_test;
one thread per seed, writes via mapped device pointer with
__threadfence_system() for PCIe coherence.
- argmax_eq_test, compute_sigma_c51/iqn_test: __threadfence_system()
added before kernel exit.
Test refactor (distributional_q_tests.rs):
- MappedI32Buffer helper (test-utility version of the production
f32-only MappedBuffer).
- Single batched launch per test instead of N launches.
- Tests 0.A and 0.B preserved assertions; runtime drops from ~1.86s
(Test 0.A) and ~3.8s (Test 0.B) to ~0.15s each on RTX 3050 Ti.
Dead code: launch_thompson_direction (single-seed) and the OnceLock
KernelSet single-launch wrappers deleted; orphan code per
feedback_wire_everything_up.md.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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