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[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

** No longer affects: linux (Ubuntu Xenial)

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https://bugs.launchpad.net/bugs/1692538

Title:
  Ubuntu 16.04.02: ibmveth: Support to enable LSO/CSO for Trunk VEA

Status in The Ubuntu-power-systems project:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Zesty:
  Fix Released
Status in linux source package in Artful:
  Fix Released

Bug description:
  
  == SRU Justification ==
  Commit 66aa0678ef is request to fix four issues with the ibmveth driver.
  The issues are as follows:
  - Issue 1: ibmveth doesn't support largesend and checksum offload features when configured as "Trunk".
  - Issue 2: SYN packet drops seen at destination VM. When the packet
  originates, it has CHECKSUM_PARTIAL flag set and as it gets delivered to IO
  server's inbound Trunk ibmveth, on validating "checksum good" bits in ibmveth
  receive routine, SKB's ip_summed field is set with CHECKSUM_UNNECESSARY flag.
  - Issue 3: First packet of a TCP connection will be dropped, if there is
  no OVS flow cached in datapath.
  - Issue 4: ibmveth driver doesn't have support for SKB's with frag_list.

  The details for the fixes to these issues are described in the commits
  git log.



  == Comment: #0 - BRYANT G. LY <bgly@xxxxxxxxxx> - 2017-05-22 08:40:16 ==
  ---Problem Description---

   - Issue 1: ibmveth doesn't support largesend and checksum offload features
     when configured as "Trunk". Driver has explicit checks to prevent
     enabling these offloads.

   - Issue 2: SYN packet drops seen at destination VM. When the packet
     originates, it has CHECKSUM_PARTIAL flag set and as it gets delivered to
     IO server's inbound Trunk ibmveth, on validating "checksum good" bits
     in ibmveth receive routine, SKB's ip_summed field is set with
     CHECKSUM_UNNECESSARY flag. This packet is then bridged by OVS (or Linux
     Bridge) and delivered to outbound Trunk ibmveth. At this point the
     outbound ibmveth transmit routine will not set "no checksum" and
     "checksum good" bits in transmit buffer descriptor, as it does so only
     when the ip_summed field is CHECKSUM_PARTIAL. When this packet gets
     delivered to destination VM, TCP layer receives the packet with checksum
     value of 0 and with no checksum related flags in ip_summed field. This
     leads to packet drops. So, TCP connections never goes through fine.

   - Issue 3: First packet of a TCP connection will be dropped, if there is
     no OVS flow cached in datapath. OVS while trying to identify the flow,
     computes the checksum. The computed checksum will be invalid at the
     receiving end, as ibmveth transmit routine zeroes out the pseudo
     checksum value in the packet. This leads to packet drop.

   - Issue 4: ibmveth driver doesn't have support for SKB's with frag_list.
     When Physical NIC has GRO enabled and when OVS bridges these packets,
     OVS vport send code will end up calling dev_queue_xmit, which in turn
     calls validate_xmit_skb.
     In validate_xmit_skb routine, the larger packets will get segmented into
     MSS sized segments, if SKB has a frag_list and if the driver to which
     they are delivered to doesn't support NETIF_F_FRAGLIST feature.

  Contact Information = Bryant G. Ly/bgly@xxxxxxxxxx

  ---uname output---
  4.8.0-51.54

  Machine Type = p8

  ---Debugger---
  A debugger is not configured

  ---Steps to Reproduce---
   Increases performance greatly

  The patch has been accepted upstream:
  https://patchwork.ozlabs.org/patch/764533/

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