netdev - Re: A performance regression of gretap

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Message-ID: <1373509919.12250.6.camel@cr0>
Date:	Thu, 11 Jul 2013 10:31:59 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Pravin Shelar <pshelar@...ira.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: A performance regression of gretap

On Wed, 2013-07-10 at 19:28 -0700, Pravin Shelar wrote:
> On Wed, Jul 10, 2013 at 7:15 PM, Cong Wang <amwang@...hat.com> wrote:
> > On Wed, 2013-07-10 at 06:01 -0400, Cong Wang wrote:
> >>
> >> Could you please take a look? And, gre tunnel is fine, this
> >> problem only exists for gretap. I reviewed the gretap code,
> >> but can't find any bug.
> >
> > After digging it a little bit, I found some of the packets on RX side
> > have incorrect TCP checksum after going through gretap, while the
> > packets captured on eth0 are all correct.
> >
> > Thanks.
> >
> I do not see it on my end.
> Can you tell me NIC type and features set for eth device?

Sure, it is virtio_net which is not able to do rx checksum, therefore
->ip_summed is CHECKSUM_NONE.

# ethtool -i eth0
driver: virtio_net
version: 1.0.0
firmware-version: 
bus-info: 0000:00:08.0
supports-statistics: no
supports-test: no
supports-eeprom-access: no
supports-register-dump: no
supports-priv-flags: no

# ethtool -k eth0
Offload parameters for eth0:
rx-checksumming: off
tx-checksumming: on
scatter-gather: on
tcp-segmentation-offload: on
udp-fragmentation-offload: on
generic-segmentation-offload: on
generic-receive-offload: on
large-receive-offload: off
rx-vlan-offload: off
tx-vlan-offload: off
ntuple-filters: off
receive-hashing: off


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