Comment 21 for bug 1692538

Hi Frank,

Yes, that is how I see it - these changes can go through, but we need
good docs to point people to as there is an incredibly high likelihood
of misconfiguration at various points.

Regards,
Daniel

On Tue, Dec 19, 2017 at 3:46 AM, Frank Heimes
<email address hidden> wrote:
> Siva and Daniel, may I just ask where we are on this?
> Well it looks to me that Siva/IBM sees this more as a miss-configuration, so that the changes in comment #18 are _not_ needed. Daniel, do you see it now the same way?
> But in this case this needs to be documented somewhere, so that we can point customers, too it - right?
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> 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:
> In Progress
> Status in linux package in Ubuntu:
> Fix Released
> Status in linux source package in Xenial:
> In Progress
> 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 <email address hidden> - 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. <email address hidden>
>
> ---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/
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/ubuntu-power-systems/+bug/1692538/+subscriptions