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

[Ananyev, Konstantin]

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Ananyev, Konstantin
> Sent: Wednesday, August 30, 2017 10:39 AM
> To: Kavanagh, Mark B <mark.b.kavanagh at intel.com>; Hu, Jiayu <jiayu.hu at intel.com>
> Cc: dev at dpdk.org; Tan, Jianfeng <jianfeng.tan at intel.com>
> Subject: Re: [dpdk-dev] [PATCH 2/5] gso/lib: add TCP/IPv4 GSO support
> 
> 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

s/unavailable/unavoidable/
sorry for bad typing.
Konstantin

> >
> > Thanks,
> > Mark
> >