[dpdk-dev] [PATCH 2/5] gso/lib: add TCP/IPv4 GSO support

[Ananyev, Konstantin]

Hi Mark,

> >> > +
> >> > +void
> >> > +gso_parse_packet(struct rte_mbuf *pkt)
> >>
> >> There is a function rte_net_get_ptype() that supposed to provide similar
> >functionality.
> >> So we probably don't need to create a new SW parse function here, instead
> >would be better
> >> to reuse (and update if needed) an existing one.
> >> Again user already might have l2/l3/l4.../_len and packet_type setuped.
> >> So better to keep SW packet parsing out of scope of that library.
> >
> >Hmm, I know we have discussed this design choice in the GRO library, and I
> >also think it's
> >better to reuse these values.
> >
> >But from the perspective of OVS, it may add extra overhead, since OVS doesn't
> >parse every
> >packet originally. Maybe @Mark can give us more inputs from the view of OVS.
> 
> Hi Jiayu, Konstantin
> 
> For GSO, the application needs to know:
> - the packet type (as it only currently supports TCP/IPv4, VxLAN, GRE packets)
> - the l2/3/4_lens, etc. (in order to replicate the original packet's headers across outgoing segments)
> 
> For this, we can use the rte_net_get_ptype function, as per Konstantin's suggestion, as it provides both - thanks Konstantin!
> 
> WRT the extra overhead in OvS: TSO is the defacto standard, and GSO is provided purely as a fallback option. As such, and since the
> additional packet parsing is a necessity in order to facilitate GSO, the additional overhead is IMO acceptable.

As I remember, for TSO in DPDK user still have to provide l2/l3/l4_len and mss information to the PMD.
So unless user knows these value straightway (user creates a packet himself) some packet processing will be unavailable anyway.
Konstantin
> 
> Thanks,
> Mark
>