Receiver Checksum Offloading

• Optimization essentially “Free”, but NIC hardware must support it.
• Details for Trapeze implementation:
  • Firmware accumulates partial checksum for payload portion of message
    • Obtains partial checksums from lanai-host DMA engines
  • Driver swizzles headers & computes header checksum
  • Driver adds payload & header checksum
  • M_HWCKSUM Flag set in mbuf header if checksum is correct (e.g., 0)
  • in_cksum() routines modified to skip checksum if header has M_HWCKSUM set

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