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From: Franck Baudin <franck.baudin@qosmos.com>
To: "Xie, Huawei" <huawei.xie@intel.com>,
	 "Gray, Mark D" <mark.d.gray@intel.com>,
	Thomas Monjalon <thomas.monjalon@6wind.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	"dpdk-ovs@lists.01.org" <dpdk-ovs@lists.01.org>
Subject: Re: [dpdk-dev] Wrong TCP checksum of packets sent by Linux guest (virtIO/vhost)
Date: Wed, 03 Sep 2014 16:12:56 +0200
Message-ID: <540721E8.2010307@qosmos.com> (raw)
In-Reply-To: <C37D651A908B024F974696C65296B57B0F284EE2@SHSMSX101.ccr.corp.intel.com>

Hi,

On 09/03/14 13:13, Xie, Huawei wrote:
> Looping in the dpdk-ovs list.
>
> * Does the new vhost API allow a user to know if all the relevant offloads have
> been
> turned on/off for that interface? It seems that this is possible through the
> virtio_net
> structure but it would be good to get some feedback from the relevant person
> working on DPDK (Huawei?).
>
> * If this is the case, then it is probably in the realm of the vswitch do the actual
> checksum (for VM-VM) or correctly configure the NIC when sending out through
> the physical interface.
>
> Comments?
>
> Mark:
> So far not supported. This is important as well in VxLan case. For the packet flow
> Guest A->  virtio -> ..->OVDK->.. -> Guest B.
> 1) If guest A and B are on different host machines, say A and B respectively,  and if the nic on A supports
> vxlan checksum offload, then both guest and host needn't generate checksum, the nic will
> generate checksum for both inner and outer packet.
> 2) In VM2VM case, as it is trusted communication channel, could we negotiate with the guest tcp stack not to verify checksum
> for received packet?
The problem is that any TCP packet send by a vanilla Linux guest through 
vhost is incorrect (VM to anything, including other colocalied VMs). In 
other words, the VM cannot use TCP. QEMU options and ethtool -K csum off 
tso off ("TCP stack negociation") have no effect, maybe because the 
vhost backend is misbehaving.

Franck

  reply	other threads:[~2014-09-03 14:08 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-02 13:20 Franck BAUDIN
2014-09-02 13:29 ` Thomas Monjalon
2014-09-02 14:37   ` Franck Baudin
2014-09-03 10:00   ` Gray, Mark D
2014-09-03 11:13     ` Xie, Huawei
2014-09-03 14:12       ` Franck Baudin [this message]
2014-09-03 16:07         ` Gray, Mark D
2014-09-04  2:54         ` Xie, Huawei
2014-09-04  9:24           ` Franck Baudin
2014-09-04 10:35             ` Xie, Huawei
2014-09-03 16:15       ` Gray, Mark D

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