> -----Original Message----- > From: Maxime Coquelin [mailto:maxime.coque...@redhat.com] > Sent: Saturday, April 8, 2017 12:41 AM > To: Tan, Jianfeng; acon...@redhat.com; so...@sonusnet.com; > yuanhan....@linux.intel.com; thomas.monja...@6wind.com; dev@dpdk.org > Subject: Re: [PATCH v3 7/9] net/virtio: Add MTU feature support > > Hi Jianfeng, > > On 04/05/2017 04:50 PM, Tan, Jianfeng wrote: > > > > > > On 4/5/2017 9:54 PM, Maxime Coquelin wrote: > >> > >> > >> On 04/05/2017 11:42 AM, Tan, Jianfeng wrote: > >>> Hi Maxime, > >>> > >>> Thank you for replying. > >>> > >>> On 4/5/2017 3:11 PM, Maxime Coquelin wrote: > >>>> Hi Jianfeng, > >>>> > >>>> On 04/05/2017 06:52 AM, Tan, Jianfeng wrote: > >>>>> Hi Maxime, > >>>>> > >>>>> Have some confusion about this feature. Please help confirm. > >>>>> > >>>>> (1) With this feature, we only support to advertise MTU value which is > >>>>> defined by QEMU to frontend and backend driver separately. (2) But > it > >>>>> does not allow frontend driver to set a different MTU to QEMU and > then > >>>>> to vhost backend. > >>>>> > >>>>> Correct? > >>>>> If it's correct, why not MTU works like (2)? > >>>> > >>>> Because idea is that the hosts advertises the maximum MTU value it > >>>> supports. The frontend driver is free to use a smaller value. The goal > >>>> of this change is to make possible to set a uniform MTU value across > >>>> the infrastructure, the management tools giving a hint to the guests on > >>>> the MTU value it should use. > >>> > >>> Based on that MTU is the maximum packet size that can be sent instead > of > >>> that can be received: > >>> (1) Why vhost (as a device) does not drop any packets which are longer > >>> than MTU when dequeue()? > >> That's a good point. > >> As when MTU value is negotiated, the guest agrees not to send larger > >> packets. But we cannot trust the guest, so vhost needs to check the > >> packet length. > >> > >>> (2) See some NICs also use MTU to calculate maximum packet size that > can > >>> be received, like ixgbe, i40e, shall we also do that? > >> Can you give me some pointers to the code? > > > > Please refer ixgbe_dev_mtu_set(), and i40e_dev_mtu_set(). > > Thanks. Yes, we could also do that. > > I can send a patch for this and another one to check the size of the > packet respects negotiated MTU value. Or maybe you want to do this?
I'll help review then. Thanks, Jianfeng
