Re: [dpdk-dev] [PATCH v4 8/8] virtio/lib:add guest offload handle

[Thomas Monjalon <thomas.monjalon@6wind.com>]

Yuanhan,
You deserve a "review award"!
Thanks a lot

2015-11-11 16:23, Yuanhan Liu:
> Regarding to your patch title, there are two minor pits:
> 
> - the prefix should be "vhost" but not "virtio/lib".
> 
> - you should add an extra space after ":"
> 
> On Wed, Nov 11, 2015 at 02:40:46PM +0800, Jijiang Liu wrote:
> > Enqueue guest offload(CSUM and TSO) handle.
> 
> (ALL) Your patch lacks some explanation. And I don't think it's about
> guest offload handling, it's about setting the right offload fields for
> RX side, such as VIRTIO_NET_HDR_F_NEEDS_CSUM.
> 
> And you need spend few words to state why that is required. Something
> like following might help others to review:
> 
>     For packet going through from one VM to another VM without passing
>     the NIC, and the VM claiming that it supports checksum offload,
>     no one will actually calculate the checksum, hence, the packet
>     will be dropped at TCP layer, due to checksum validation is failed.
> 
>     However, for VM2VM case, there is no need to do checksum, for we
>     think the data should be reliable enough, and setting VIRTIO_NET_HDR_F_NEEDS_CSUM
>     at RX side will let the TCP layer to bypass the checksum validation,
>     so that the RX side could receive the packet in the end.
> 
>     At RX side, the offload information is inherited from mbuf, which is
>     in turn inherited from TX side. If we can still get those info at RX
>     side, it means the packet is from another VM at same host.  So, it's
>     safe to set the VIRTIO_NET_HDR_F_NEEDS_CSUM, to skip checksum validation.
> 
> 
> > Signed-off-by: Jijiang Liu <jijiang.liu@intel.com>
> > ---
> >  lib/librte_vhost/vhost_rxtx.c |   45 +++++++++++++++++++++++++++++++++++++++-
> >  1 files changed, 43 insertions(+), 2 deletions(-)
> > 
> > diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
> > index 9e70990..468fed8 100644
> > --- a/lib/librte_vhost/vhost_rxtx.c
> > +++ b/lib/librte_vhost/vhost_rxtx.c
> > @@ -54,6 +54,42 @@ is_valid_virt_queue_idx(uint32_t idx, int is_tx, uint32_t qp_nb)
> >  	return (is_tx ^ (idx & 1)) == 0 && idx < qp_nb * VIRTIO_QNUM;
> >  }
> >  
> > +static void
> > +virtio_enqueue_offload(struct rte_mbuf *m_buf, struct virtio_net_hdr *net_hdr)
> > +{
> 
> As virtio_hdr is set per mbuf, you'd better reset net_hdr first before
> setting it. Otherwise, if this mbuf has no offload related stuff, you
> may still get a net_hdr with offload related fields set, due to last
> mbuf has that.
> 
> I know the chance is rare, but it's for code logic.
> 
> 
> 	--yliu