Nginx / LRO on vmxnet3 / missing ACKs

[Lukas Tribus]

> Hello,
>
> I'm currently investigating an issue with Linux (3.13.0), nginx (1.6.2),
> vmxnet3 (1.2.0.0-k-NAPI), IPv6 connections and large receive offload (LRO)
> enabled. The workflow we are investigating is a POST of a small file (jpg)
> towards a php5-fpm pool.
>
> From a network (tcpdump) point a view, it seems that when LRO is disabled on
> the vmxnet3 interface, all tcp packets are ack'ed correctly after reception.
> However, when LRO is enabled, only the request part of the POST is acked at
> tcp-level before the client retransmits the packets.

This is clearly not a userspace issue. Its either a kernel or a hypervisor issue.

I would start by using a supported and uptodate kernel, because 3.13.0 is neither.