⚡ Bolt: Use napi_alloc_skb in NAPI polling context

[maxugly]

💡 What: Replaced the generic dev_alloc_skb with the NAPI-specific napi_alloc_skb in the high-frequency packet receive path (sim_rx_dequeue). Also removed the redundant skb_reserve(skb, 2) call, as napi_alloc_skb naturally handles payload alignment to NET_IP_ALIGN.

🎯 Why: sim_rx_dequeue operates entirely within a NAPI polling softirq context. Using the generic dev_alloc_skb accesses global SLUB caches which incurs greater overhead and potential lock contention. Switching to napi_alloc_skb utilizes per-CPU cache mechanisms designed specifically to accelerate NAPI packet reception, making allocations faster and reducing fragmentation during packet floods.

📊 Impact: Reduces memory allocation overhead in the critical receive data path, lowering CPU utilization and improving peak packet ingestion rates on high-speed hardware or concurrent simulated workloads. Code is also slightly cleaner due to built-in alignment handling.

🔬 Measurement: Validate functionality by running the NATA loopback latency and throughput benchmark using sudo ./scripts/nata-bench-once.sh. Watch for an increase in RX throughput or decrease in CPU utilization via tools like perf or observing host load under flood.

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PR created automatically by Jules for task 4844776403328240317 started by @maxugly

Summary by CodeRabbit

• Performance

  • Improved packet receive processing efficiency by using the network polling context for buffer allocation.
  • Removed unnecessary manual buffer headroom handling while preserving existing packet processing and error behavior.

• Documentation

  • Added documentation describing the optimized receive-path allocation approach.

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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: ae84cd6f-aa04-4e7c-ab00-8d08156b0699

📥 Commits

Reviewing files that changed from the base of the PR and between 514361c and 16fd8dc.

📒 Files selected for processing (2)

• .jules/bolt.md
• module/nata_blk.c

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📝 Walkthrough

Walkthrough

The RX dequeue path now uses NAPI-aware SKB allocation with exact payload sizing and removes manual headroom reservation. A dated guidance entry documents this allocation pattern.

Changes

NAPI RX allocation

Layer / File(s)	Summary
Update RX skb allocation .jules/bolt.md, module/nata_blk.c	sim_rx_dequeue uses napi_alloc_skb with the selected NAPI instance and hdr.len, while retaining existing failure cleanup; documentation describes avoiding manual alignment reserves.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• maxugly/nata#7: Updates the same RX path to use NAPI-aware allocation and adds NAPI plumbing.
• maxugly/nata#23: Applies the same allocation and manual-alignment removal with related documentation.
• maxugly/nata#21: Makes the corresponding sim_rx_dequeue allocation change and adds related guidance.

🚥 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 accurately summarizes the primary change: switching to napi_alloc_skb in a NAPI polling receive path.
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-alloc-skb-4844776403328240317

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