TCP retransmissions poor throughput and rx_no_buffer errors increasing on ibmveth NIC

Solution Unverified - Updated -

Issue

  • TCP retransmissions poor throughput and rx_no_buffer errors in ethtool -S increasing on ibmveth NIC
  • When TCP connections and TCP traffic load increases at a certain point the network is flooded with retransmissions due to packet drop which results in very poor network performance.

Environment

  • IBM pSeries POWER (ppc64) LPAR or VM
    • IBM virtual network interface card (NIC) using ibmveth driver
    • Multiple CPU cores allocated to system
    • Many concurrent TCP connections, such as a database workload

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