[Deepin-Kernel-SIG] [FROMLIST] [linux 6.6-y] net: stmmac: Optimize cache prefetch in RX path

[opsiff]

next inclusion
from next-20250122
category: performance

Current code prefetches cache lines for the received frame first, and then dma_sync_single_for_cpu() against this frame, this is wrong. Cache prefetch should be triggered after dma_sync_single_for_cpu().

This patch brings ~2.8% driver performance improvement in a TCP RX throughput test with iPerf tool on a single isolated Cortex-A65 CPU core, 2.84 Gbits/sec increased to 2.92 Gbits/sec.

Reviewed-by: Alexander Lobakin [email protected]
Reviewed-by: Yanteng Si [email protected]

Summary by Sourcery

Enhancements:

• Improve performance of the STM MAC driver.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request optimizes the cache prefetch in the RX path of the stmmac driver. The cache prefetch is moved after the dma_sync_single_for_cpu() call to ensure that the cache prefetch is triggered after the DMA synchronization.

Sequence diagram for optimized RX path cache prefetch

sequenceDiagram
    participant Driver as STMMAC Driver
    participant DMA as DMA Controller
    participant Cache as CPU Cache
    participant Memory as System Memory

    Note over Driver,Memory: Before optimization
    Driver->>Cache: Prefetch data
    Driver->>DMA: DMA sync for CPU

    Note over Driver,Memory: After optimization
    Driver->>DMA: DMA sync for CPU
    Driver->>Cache: Prefetch data
    Note right of Cache: More efficient cache usage

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Flow diagram for RX packet processing optimization

flowchart LR
    subgraph before[Before Optimization]
    A1[Receive Packet] --> B1[Prefetch Cache]
    B1 --> C1[DMA Sync]
    C1 --> D1[Process Data]
    end

    subgraph after[After Optimization]
    A2[Receive Packet] --> B2[DMA Sync]
    B2 --> C2[Prefetch Cache]
    C2 --> D2[Process Data]
    end

    before -.-> after
    style before fill:#f9f,stroke:#333
    style after fill:#9f9,stroke:#333

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File-Level Changes

Change	Details	Files
Move cache prefetch after dma_sync_single_for_cpu()	Removed the prefetch before dma_sync_single_for_cpu(). Added the prefetch after dma_sync_single_for_cpu().	drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

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[sourcery-ai]

Hey @opsiff - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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