Re: [lvs-users] can somebody explain how gro (generic receive offload) b

To: " users mailing list." <lvs-users@xxxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [lvs-users] can somebody explain how gro (generic receive offload) bothers lvs? (kernel 2.6.32)
From: Thomas Bätzler <t.baetzler@xxxxxxxxxx>
Date: Tue, 11 Dec 2012 22:00:35 +0100

Zhongkang Lao wrote on 05.12.2012 08:41:
> I have already googled this like a hundred of times, but I got nothing.
> I didn't find any page or any article explain this.
> I'm sure someone here can explain this.
> So sorry to bother you guys here.

I don't have any answers, but I can confirm the problem (and the
workaround) on a box running Debian "Squeeze" with 2.6.32 directing
traffic from a VIP bound to lo via NAT to an active/backup bonding
interface on the backend. With "gro on" for the bonded interfaces to the
backend real servers, throughput was ~64K/s. With "gro off" it was
~50MB/s. It's not a general networking problem since a direct connection
to the real server via a DNAT port forward was not impacted.

>From what I gleaned from a cursory look with tcpdump it seems that the
problem is caused by incorrectly calculated tcp checksums.

Anybody interested in pursuing this further?


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