[dpdk-dev] [PATCH v3 1/7] ethdev: introduce Tx generic tunnel L3/L4 offload

[Xueming(Steven) Li]

> -----Original Message-----
> From: Yongseok Koh
> Sent: Wednesday, March 21, 2018 9:41 AM
> To: Xueming(Steven) Li <xuemingl at mellanox.com>
> Cc: Wenzhuo Lu <wenzhuo.lu at intel.com>; Jingjing Wu <jingjing.wu at intel.com>;
> Thomas Monjalon <thomas at monjalon.net>; Olivier MATZ
> <olivier.matz at 6wind.com>; Shahaf Shuler <shahafs at mellanox.com>; Ferruh
> Yigit <ferruh.yigit at intel.com>; dev at dpdk.org
> Subject: Re: [PATCH v3 1/7] ethdev: introduce Tx generic tunnel L3/L4
> offload
> 
> On Mon, Mar 05, 2018 at 10:51:15PM +0800, Xueming Li wrote:
> > This patch introduce new TX offload flags for device that supports
> > tunnel agnostic L3/L4 checksum and TSO offload.
> >
> > The support from the device is for inner and outer checksums on
> > IPV4/TCP/UDP and TSO for *any packet with the following format*:
> >
> > < some headers > / [optional IPv4/IPv6] / [optional TCP/UDP] / <some
> > headers> / [optional inner IPv4/IPv6] / [optional TCP/UDP]
> >
> > For example the following packets can use this feature:
> >
> > 1. eth / ipv4 / udp / VXLAN / ip / tcp 2. eth / ipv4 / GRE / MPLS /
> > ipv4 / udp
> >
> > Signed-off-by: Xueming Li <xuemingl at mellanox.com>
> > ---
> >  lib/librte_ether/rte_ethdev.h | 24 ++++++++++++++++++++++++
> >  lib/librte_mbuf/rte_mbuf.c    |  5 +++++
> >  lib/librte_mbuf/rte_mbuf.h    | 18 ++++++++++++++++--
> >  3 files changed, 45 insertions(+), 2 deletions(-)
> >
> > diff --git a/lib/librte_ether/rte_ethdev.h
> > b/lib/librte_ether/rte_ethdev.h index 036153306..66d12d3e0 100644
> > --- a/lib/librte_ether/rte_ethdev.h
> > +++ b/lib/librte_ether/rte_ethdev.h
> > @@ -980,6 +980,30 @@ struct rte_eth_conf {
> >   *   the same mempool and has refcnt = 1.
> >   */
> >  #define DEV_TX_OFFLOAD_SECURITY         0x00020000
> > +/**< Generic tunnel L3/L4 checksum offload. To enable this offload
> > +feature
> > + * for a packet to be transmitted on hardware supporting generic
> > +tunnel L3/L4
> > + * checksum offload:
> > + *  - fill outer_l2_len and outer_l3_len in mbuf
> > + *  - fill l2_len and l3_len in mbuf
> > + *  - set the flags PKT_TX_TUNNEL_xxx (use PKT_TX_TUNNEL_UNKNOWN if
> > +undefined)
> > + *  - set the flags PKT_TX_OUTER_IP_CKSUM
> > + *  - set the flags PKT_TX_IP_CKSUM
> > + *  - set the flags PKT_TX_TCP_CKSUM, PKT_TX_SCTP_CKSUM or
> > +PKT_TX_UDP_CKSUM  */
> > +#define DEV_TX_OFFLOAD_GENERIC_TNL_CKSUM	0x00040000
> 
> It looks redundant to me. Isn't it same as having DEV_TX_OFFLOAD_*_CKSUM?
> According to the API document, when PKT_TX_*_CKSUM is set, all the
> necessary length fields should be filled in (e.g. mbuf->outer_l?_len and
> mbuf->l?_len). It doesn't need to specify any tunnel type for checksum.
> For example, in order to request checksum offload for an unknown tunnel
> type which is similar to VxLAN, what should app do? Even without defining
> this new offload flag, it is currently possible by setting
> 	(PKT_TX_OUTER_IP_CKSUM | PKT_TX_OUTER_IPV4 | PKT_TX_IP_CKSUM |
> 	 PKT_TX_IPV4 | PKT_TX_UDP_CKSUM)
> along with various length fields.

Agree it almost same as existing checksum offloading requirement, besides:
1. it does not demand pseudo checksum
2. no need to clear IP checksum
I guess the requirement on API doc is a super set and differences could be 
documented on PMD doc.

For mlx5 original chksum offloading, hw will parse everything w/o demanding
mbuf headers, a little better performance than SWP. The question is how to 
choose between SWP and HW checksum offloading - assuming PKT_TX_TUNNEL_UNKNOWN
is the key. Take L3 VXLAN(no inner L2 header) as example, only SWP could 
offload it correctly and PKT_TX_TUNNEL_UNKOWN should be used here, not 
PKT_TX_TUNNEL_VXLAN, make sense?

Another question, how does user app know the NIC capability of generic tunnel 
checksum offload?

> 
> > +/**< Generic tunnel segmentation offload. To enable it, the user needs
> to:
> > + *  - fill outer_l2_len and outer_l3_len in mbuf
> > + *  - fill l2_len and l3_len in mbuf
> > + *  - set the flags PKT_TX_TUNNEL_xxx (use PKT_TX_TUNNEL_UNKNOWN if
> > +undefined)
> > + *  - set the flags PKT_TX_OUTER_IPV4 or PKT_TX_OUTER_IPV6
> > + *  - if it's UDP tunnel, set the flags PKT_TX_OUTER_UDP
> > + *  - set the flags PKT_TX_IPV4 or PKT_TX_IPV6
> > + *  - set the PKT_TX_TCP_SEG flag in mbuf->ol_flags (this flag implies
> > + *    PKT_TX_OUTER_IP_CKSUM, PKT_TX_IP_CKSUM and PKT_TX_TCP_CKSUM)
> > + * Hardware that supports generic tunnel TSO offload only update
> > +outer/inner
> > + * L3/L4 fields, tunnel fields are not touched.
> > + */
> > +#define DEV_TX_OFFLOAD_GENERIC_TNL_TSO		0x00080000
> 
> Practically, for the existing TSO offloads for tunneled packets, tunnel
> type
> (PKT_TX_TUNNEL_*) is needed for knowing if transport is UDP-based or IP-
> based because the length field of UDP header should be updated for TSO.
> AFAIK, there's no TCP-based tunnel. For PKT_TX_TUNNEL_UNKNOWN, the only
> thing _unknown_ seems to be the type of transport and by defining
> PKT_TX_OUTER_UDP, you seem to recognize the type of transport between UDP
> and IP (it's not non-UDP). Given that, the new flags still look redundant
> and ambiguous. If PKT_TX_TUNNEL_VXLAN is set, there's no need to set
> PKT_TX_OUTER_UDP redundantly.
> 
> Instead, I think defining PKT_TX_TUNNEL_UDP_UNKNOWN and
> PKT_TX_TUNNEL_IP_UNKNOWN could be a good alternative. It is only my humble
> two cents and I'd like to hear from more people regarding this.
> 

This flag looks more like a feature notification. Current tunnel offloading 
capability like "DEV_TX_OFFLOAD_VXLAN_TNL_TSO" ties to VXLAN tunnel type,
DEV_TX_OFFLOAD_GENERIC_TNL_TSO should be able to let users know that NIC's
capability of offloading generic tunnel type like MPLS-in-UDP that not defined
yet. PKT_TX_OUTER_UDP is something must to have to flag an exists of outer UDP
in such case.

> 
> Thanks,
> Yongseok