Upstream PR 2929 Deferred PGRAPH IRQ

Upstream PR #2929 — Defer PGRAPH IRQ delivery from PFIFO

Upstream work · Actionable research · Research and retired work

Current disposition — November 1, 2026

Reviewed: November 1, 2026. Fork source: b7140848 (full SHA b71408480a3a979a9c584663e1d1f400904c8bb7). Latest stable checked: v0.8.136-0-g458730bf5373, September 30, source 458730bf5373f1f0d027450fef7443e3af7a3ae1. GitHub state, branch recommendation, source presence and release availability are separate facts. See current status and release versus main.

Current field	November 1, 2026 observation
GitHub source	Upstream #2929
GitHub state / draft	Open / No
Current head	4316955c55ad1d9778cdb9a1143e6c0929b57df3
Originally reviewed head	4316955c55ad1d9778cdb9a1143e6c0929b57df3
Last metadata update (UTC)	2026-10-18T20:59:12Z
Head versus original review	Same recorded head; metadata/state updates do not indicate a new proposal-code head.
Current action	Open proposal; refresh integration and focused tests before handoff.
Fork/release availability	This upstream proposal’s GitHub state does not establish full fork/release inclusion. The historical overlap below is scoped to its recorded fork baseline; use the current feature register for delivered fork behavior.

The current head matches the recorded September review head. Later updated_at metadata does not establish changed proposal code. The original fork overlap remains a dated source comparison, not a fresh integration or native qualification result.

This refresh checked GitHub identity/state and the specific source boundaries named above. It did not rerun native games, XISO timings or integration qualification. Historical performance claims remain attached to their original heads.

Historical review — September 21, 2026

The review below is preserved as written, including its original state, head, fork baseline and proposed handoff. Its present-tense statements apply to that dated review; the current disposition above governs today’s action.

← Upstream Work

Field	Value
Upstream PR	xemu-project/xemu#2929
State at 2026-09-21 audit	Open
Reviewed upstream head	4316955c55ad1d9778cdb9a1143e6c0929b57df3
Last upstream update seen	2026-09-06
Reviewed upstream base	f9b14039e5bb56ae2d8f028e31e7cc19f13f7e12
Fork baseline	82d04d84bdb3de956f20c3537e1da2cece0e8da2
Relationship	Related lock-order work, distinct path
Related fork work	Mainkill1/xemu#132
Contribution priority	Medium
Upstream contact status	No comment posted by this audit.

Summary

Upstream defers PGRAPH interrupt delivery from the PFIFO thread to avoid a load-time hang. Fork #132 repairs PFIFO/PGRAPH inversion during renderer switching.

Upstream scope

The interrupt path has its own lock and execution-context dependencies; deferral moves delivery to a safer context.

Corresponding fork work

Fork #132 provides a production-linked phase model and deterministic concurrency tests for dropping PGRAPH before PFIFO reacquisition, servicing pending work, framebuffer handoff, and renderer replacement.

Difference that must remain explicit

Renderer handoff and IRQ delivery are distinct lock cycles. A clean renderer-switch test does not prove the interrupt path deadlock-free.

Transferable regression and review cases

• Draw the exact lock graph for IRQ raise and bottom-half delivery.
• Force the reported PFIFO/PGRAPH interleaving with barriers rather than timeout-based scheduling.
• Verify interrupt level/edge semantics and no lost or duplicate delivery.
• Retain PFIFO-held callback return contracts where required.

Suggested upstream handoff

Offer #132’s deterministic lock-order fixture pattern, not its renderer-switch implementation as a direct fix.

Claims this page does not support

• It does not prove the upstream branch merges cleanly with current upstream.
• It does not prove a native correctness or performance result unless a linked exact-head run says so.
• It does not transfer favorable performance percentages between hardware, renderers, games, or source heads.
• It does not authorize posting a comment or review upstream.

Before sending anything upstream

• Refresh the PR state, head SHA, description, changed files, and newest review comments.
• Recheck the corresponding fork implementation on current main.
• Run or cite the narrow regression on an exact source state.
• Verify every public link and remove private paths, captures, game data, credentials, and internal logs.
• Phrase source concerns as source concerns and reproductions as reproductions.
• State the uncovered behavior and evidence limit.
• Add the posted URL and upstream response to this page.

Tracking log

Date	Upstream head	Action	Result
2026-09-21	4316955c55ad	Fork/upstream source comparison recorded	Handoff prepared; nothing posted

References

• Upstream PR #2929
• Fork repository
• Upstream Work
• Pull Request Lessons