Fix: scope A5 CPU topology fallback to x86 standard cards

[sunkaixuan2018]

Summary

• use the AICPU OCCUPY fallback only when CPU_TOPO is unavailable on the verified x86 Ascend950PR_9579 standard-card signature (OCCUPY=0x3e)
• preserve the existing failure behavior for unverified hosts, SoCs, and masks while keeping the normal CPU_TOPO path unchanged
• cover accepted and rejected signatures in the focused C++ regression test and document the compatibility boundary

Testing

• git diff --check upstream/main...HEAD
• previous A5 hardware validation on the same Ascend950PR_9579 / OCCUPY=0x3e environment: test_a5_aicpu_topology_fallback passed and two-device onephase AllReduce passed in 15.11s
• Linux/macOS PR CI (running after this update)

[coderabbitai]

Important

Review skipped

Auto incremental reviews are disabled on this repository.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 0db14cee-917b-4a53-a790-966e0aa37d41

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

📝 Walkthrough

Walkthrough

A5 host topology probing now falls back to deriving non-SMT CPU metadata from the OCCUPY bitmap when CPU_TOPO is unsupported. Documentation and no-hardware unit tests cover topology derivation, affinity ordering, and empty masks.

Changes

A5 CPU topology fallback

Layer / File(s)	Summary
Topology fallback implementation src/a5/platform/onboard/host/aicpu_topology_probe.*, src/a5/docs/hardware.md	Topology probing derives CPU, cluster, and die metadata from set OCCUPY bits when CPU_TOPO is unavailable, with updated API documentation and compatibility details.
Fallback validation and test wiring tests/ut/cpp/a5/test_aicpu_topology_fallback.cpp, tests/ut/cpp/CMakeLists.txt	No-hardware tests validate derived metadata, allowed-CPU ordering, and empty-mask rejection; CMake registers the test target.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Poem

I’m a rabbit hopping through bits in a row,
Mapping each CPU where the OCCUPY lights glow.
CPU_TOPO may hide, but the fallback is bright,
Clusters and dies now line up just right.
Tests thump their paws: the pool’s in sight!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title matches the main change: scoping A5 CPU topology fallback to verified standard cards.
Description check	✅ Passed	The description clearly relates to the fallback behavior, test coverage, and documentation changes.

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/a5/platform/onboard/host/aicpu_topology_probe.cpp`:
- Around line 179-192: Restrict the OCCUPY fallback in
derive_topology_from_occupy to verified CPU_TOPO-capable drivers, or validate
each set host mask bit against the device-side user pool and SMT topology before
assigning phy_cpu_id and hyperthread_id. Update the corresponding
contract/documentation in src/a5/platform/onboard/host/aicpu_topology_probe.h
(lines 37-50) and src/a5/docs/hardware.md (lines 165-169) to state this
restriction; apply the implementation change at
src/a5/platform/onboard/host/aicpu_topology_probe.cpp (lines 179-192).

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 818eba7d-e086-4c4a-8af3-fdf7e676487e

📥 Commits

Reviewing files that changed from the base of the PR and between 96d0291 and 2dfba39.

📒 Files selected for processing (5)

• src/a5/docs/hardware.md
• src/a5/platform/onboard/host/aicpu_topology_probe.cpp
• src/a5/platform/onboard/host/aicpu_topology_probe.h
• tests/ut/cpp/CMakeLists.txt
• tests/ut/cpp/a5/test_aicpu_topology_fallback.cpp