7a1b6b3306
The Phase-C VdSwap PM4 ring path (commit82f3d61) emits two "PM4_XE_SWAP not consumed by drain" warnings when running: exec sylpheed.iso --ui --quiet --halt-on-deadlock \ --parallel --reservations-table Lockstep -n 100M never trips it. Two distinct race windows: (a) Inline backend (--ui forces it): drain(mem, 4096) hit its fixed packet cap before reaching the PM4_XE_SWAP we'd just injected at the WPTR tail. With 6 CPU threads, the ring accumulates >4096 packets between vd_swap callbacks. (b) Threaded backend (--parallel without --ui): the worker's DrainFence handler has a 900 ms deadline and game-batched IBs (8-10 M packets observed) keep it from reaching the tail in any reasonable budget. If the worker eventually drained past the injected packet later, the safety-net direct notify would double-count. Three changes: * gpu_system.rs: new `drain_until_wptr(target, time_budget)` draining by the canary `WorkerThreadMain` predicate (read_offset != target) instead of a fixed packet count. 900 ms deadline mirrors the threaded DrainFence handler. * handle.rs: inline `drain_to_current_wptr` switches to `drain_until_wptr`. DrainFence handler publishes the digest mirror BEFORE replying so the CPU's post-drain `digest_snapshot` sees fresh stats. * exports.rs (vd_swap): skip the PM4 ring injection unconditionally and route swap notification through `notify_xe_swap` directly. Tail-injection is unreliable under --parallel for both backends. The slot-0 fetch-constant patch is deferred (GPUBUG-FETCH-PATCH-001); draws=0 today so a stale slot 0 has no observable effect. Verification: * cargo test --workspace --release: 556 passing (unchanged). * Lockstep -n 100M --stable-digest: bit-identical to pre-fix master HEADaa3f1d3. {instructions:100000002, imports:987685, unimpl:0, draws:0, swaps:2, ...} * check --parallel --reservations-table -n 30M: 0 warnings (was 2). swaps=2. * exec --gpu-inline --parallel --reservations-table -n 30M: 0 warnings (was 2 with drained=8M-10M observed). swaps=2. Audit IDs: GPUBUG-DRAIN-001 (closed), GPUBUG-FETCH-PATCH-001 (filed, deferred). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>