⚡ Bolt: Use napi_alloc_skb for RX path performance

[maxugly]

What:
Replaced dev_alloc_skb with napi_alloc_skb in the sim_rx_dequeue function and removed the manual skb_reserve call since napi_alloc_skb automatically handles NET_IP_ALIGN.

Why:
The RX path operates in a NAPI polling context. dev_alloc_skb uses a generic slab allocator which can cause lock contention. napi_alloc_skb uses NAPI-specific per-CPU caches, providing faster sk_buff allocations during high-speed packet reception.

Impact:
Significantly reduces CPU overhead and lock contention during network packet receiving, increasing RX throughput and reducing latency.

Measurement:
Compare the iperf3 RX bandwidth between nata-a and nata-b nodes using scripts/nata-ns-up.sh before and after the change, or check CPU utilization of softirqd under heavy RX load.

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PR created automatically by Jules for task 14843957356728935227 started by @maxugly

Summary by CodeRabbit

• Bug Fixes
  • Improved receive-packet allocation during network polling.
  • Removed unnecessary packet alignment handling while preserving existing behavior when allocation fails.
• Documentation
  • Added guidance on using the appropriate packet allocator for network polling contexts.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 49ca28a0-5dc0-4c03-8345-4b6f8993e209

📥 Commits

Reviewing files that changed from the base of the PR and between 514361c and 67260b8.

📒 Files selected for processing (2)

• .jules/bolt.md
• module/nata_blk.c

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📝 Walkthrough

Walkthrough

The RX dequeue path now selects the relevant NAPI context and uses napi_alloc_skb without manual alignment reservation. Allocation failure handling is unchanged, and .jules/bolt.md documents the NAPI allocator guidance.

Changes

NAPI RX allocator

Layer / File(s)	Summary
Integrate per-NAPI skb allocation module/nata_blk.c, .jules/bolt.md	sim_rx_dequeue() selects napi0 or napi1, allocates with napi_alloc_skb, removes the fixed skb_reserve step, preserves failure handling, and documents the NAPI allocation rule.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related PRs

• maxugly/nata#21: Updates the same RX path to use per-NAPI allocation and remove manual alignment.
• maxugly/nata#11: Implements and documents the same allocator transition.
• maxugly/nata#7: Overlaps on the NAPI allocator and function-context changes.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: switching the RX path to napi_alloc_skb for performance.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch bolt-napi-skb-alloc-14843957356728935227

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