[dpdk-dev] [EXT] Re: [PATCH 1/3] mbuf: add Tx offloads for packet marking

[Olivier Matz]

On Mon, May 04, 2020 at 01:57:06PM +0530, Nithin Dabilpuram wrote:
> Hi Olivier,
> 
> On Mon, May 04, 2020 at 10:06:34AM +0200, Olivier Matz wrote:
> > External Email
> > 
> > ----------------------------------------------------------------------
> > Hi,
> > 
> > On Fri, May 01, 2020 at 04:48:21PM +0530, Jerin Jacob wrote:
> > > On Fri, Apr 17, 2020 at 12:53 PM Nithin Dabilpuram
> > > <nithind1988 at gmail.com> wrote:
> > > >
> > > > From: Nithin Dabilpuram <ndabilpuram at marvell.com>
> > > >
> > > > Introduce PKT_TX_MARK_IP_DSCP, PKT_TX_MARK_IP_ECN
> > > > and PKT_TX_MARK_VLAN_DEI Tx offload flags to support
> > > > packet marking.
> > > >
> > > > When packet marking feature in Traffic manager is enabled,
> > > > application has to the use the three new flags to indicate
> > > > to PMD on whether packet marking needs to be enabled on the
> > > > specific mbuf or not. By setting the three flags, it is
> > > > assumed by PMD that application has already verified the
> > > > applicability of marking on that specific packet and
> > > > PMD need not perform further checks as per RFC.
> > > >
> > > > Signed-off-by: Krzysztof Kanas <kkanas at marvell.com>
> > > > Signed-off-by: Nithin Dabilpuram <ndabilpuram at marvell.com>
> > > 
> > > None of the ethdev TM driver implementations has supported packet
> > > marking support.
> > > rte_tm and rte_mbuf maintainers(Christian, Oliver), Could you review this patch?
> > 
> > As you know, the number of mbuf flags is limited (only 18 bits are
> > remaining), so I think we should use them with care, i.e. for features
> > that are generic enough.
> 
> I agree, but I believe this is one of the basic flags needed like other 
> Tx checksum offload flags (like PKT_TX_IP_CKSUM, PKT_TX_IPV4, etc) which 
> are needed to identify on which packets HW should/can apply packet marking.

PKT_TX_IP_CKSUM tells the hardware to offload the checksum
calculation. This is pretty straightforward and there is no other
dependency than the offload feature advertised by the PMD.

I'm sorry, I have not a lot of experience with rte_tm.h, so it's
difficult for me to have a global view of what is done for instance when
PKT_TX_MARK_VLAN_DEI is set, and what happens when it is not set.

Can you confirm that my understanding below is correct? (or correct me
where I'm wrong)

Before your patch:
- the application enables the port and traffic manager on it
- the application calls rte_tm_mark_vlan_dei() to select which traffic
  class must be marked
- when a packet is transmitted, the traffic class is determined by the
  hardware, and if the hardware recognizes a VLAN packet, the VLAN DEI
  bit is set depending on traffic class

The problem is for packets that cannot be recognized by the hardware,
correct?

So your patch is a way to force the hardware to recognize mark set the
VLAN DEI on packets that are not recognized as VLAN packets?

How the is traffic class of the packet determined?


> > From what I understand, this feature is bound to octeontx2, so using a
> > mbuf dynamic flag would make more sense here. There are some examples in
> > dpdk repository, just grep for "dynflag".
> 
> This is not octeontx2 specific flag but any "packet marking feature" enabled
> PMD would need these flags to identify on which packets marking needs to be 
> done. This is the first PMD that supports packet marking feature and
> hence it was not exposed earlier.
> 
> For example to mark VLAN DEI, PMD cannot always assume that there is preexisting
> VLAN header from Byte 12 as there is no gaurantee that ethernet header
> always starts at Byte 0 (Custom headers before ethernet hdr).
> 
> > 
> > Also, I think that the feature availability should be advertised through
> > an ethdev offload, so an application can know at initialization time
> > that these flags can be used.
> 
> Feature availablity is already part of TM spec in rte_tm.h 
> struct rte_tm_capabilities:mark_vlan_dei_supported
> struct rte_tm_capabilities:mark_ip_ecn_[sctp|tcp]_supported
> struct rte_tm_capabilities:mark_ip_dscp_supported

Does this mean that any driver advertising this existing feature flag
has to support the new mbuf flags too? Shouldn't we have a specific
feature for it?

Please also see few comments below.

> > > > ---
> > > >  doc/guides/nics/features.rst    | 14 ++++++++++++++
> > > >  lib/librte_mbuf/rte_mbuf.c      |  6 ++++++
> > > >  lib/librte_mbuf/rte_mbuf_core.h | 36 ++++++++++++++++++++++++++++++++++--
> > > >  3 files changed, 54 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/doc/guides/nics/features.rst b/doc/guides/nics/features.rst
> > > > index edd21c4..bc978fb 100644
> > > > --- a/doc/guides/nics/features.rst
> > > > +++ b/doc/guides/nics/features.rst
> > > > @@ -913,6 +913,20 @@ Supports to get Rx/Tx packet burst mode information.
> > > >  * **[implements] eth_dev_ops**: ``rx_burst_mode_get``, ``tx_burst_mode_get``.
> > > >  * **[related] API**: ``rte_eth_rx_burst_mode_get()``, ``rte_eth_tx_burst_mode_get()``.
> > > >
> > > > +.. _nic_features_traffic_manager_packet_marking_offload:
> > > > +
> > > > +Traffic Manager Packet marking offload
> > > > +--------------------------------------
> > > > +
> > > > +Supports enabling a packet marking offload specific mbuf.
> > > > +
> > > > +* **[uses]     mbuf**: ``mbuf.ol_flags:PKT_TX_MARK_IP_DSCP``,
> > > > +  ``mbuf.ol_flags:PKT_TX_MARK_IP_ECN``, ``mbuf.ol_flags:PKT_TX_MARK_VLAN_DEI``,
> > > > +  ``mbuf.ol_flags:PKT_TX_IPV4``, ``mbuf.ol_flags:PKT_TX_IPV6``.
> > > > +* **[uses]     mbuf**: ``mbuf.l2_len``.
> > > > +* **[related] API**: ``rte_tm_mark_ip_dscp()``, ``rte_tm_mark_ip_ecn()``,
> > > > +  ``rte_tm_mark_vlan_dei()``.
> > > > +
> > > >  .. _nic_features_other:
> > > >
> > > >  Other dev ops not represented by a Feature
> > > > diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
> > > > index cd5794d..5c6896d 100644
> > > > --- a/lib/librte_mbuf/rte_mbuf.c
> > > > +++ b/lib/librte_mbuf/rte_mbuf.c
> > > > @@ -880,6 +880,9 @@ const char *rte_get_tx_ol_flag_name(uint64_t mask)
> > > >         case PKT_TX_SEC_OFFLOAD: return "PKT_TX_SEC_OFFLOAD";
> > > >         case PKT_TX_UDP_SEG: return "PKT_TX_UDP_SEG";
> > > >         case PKT_TX_OUTER_UDP_CKSUM: return "PKT_TX_OUTER_UDP_CKSUM";
> > > > +       case PKT_TX_MARK_VLAN_DEI: return "PKT_TX_MARK_VLAN_DEI";
> > > > +       case PKT_TX_MARK_IP_DSCP: return "PKT_TX_MARK_IP_DSCP";
> > > > +       case PKT_TX_MARK_IP_ECN: return "PKT_TX_MARK_IP_ECN";
> > > >         default: return NULL;
> > > >         }
> > > >  }
> > > > @@ -916,6 +919,9 @@ rte_get_tx_ol_flag_list(uint64_t mask, char *buf, size_t buflen)
> > > >                 { PKT_TX_SEC_OFFLOAD, PKT_TX_SEC_OFFLOAD, NULL },
> > > >                 { PKT_TX_UDP_SEG, PKT_TX_UDP_SEG, NULL },
> > > >                 { PKT_TX_OUTER_UDP_CKSUM, PKT_TX_OUTER_UDP_CKSUM, NULL },
> > > > +               { PKT_TX_MARK_VLAN_DEI, PKT_TX_MARK_VLAN_DEI, NULL },
> > > > +               { PKT_TX_MARK_IP_DSCP, PKT_TX_MARK_IP_DSCP, NULL },
> > > > +               { PKT_TX_MARK_IP_ECN, PKT_TX_MARK_IP_ECN, NULL },
> > > >         };
> > > >         const char *name;
> > > >         unsigned int i;
> > > > diff --git a/lib/librte_mbuf/rte_mbuf_core.h b/lib/librte_mbuf/rte_mbuf_core.h
> > > > index b9a59c8..d9f1290 100644
> > > > --- a/lib/librte_mbuf/rte_mbuf_core.h
> > > > +++ b/lib/librte_mbuf/rte_mbuf_core.h
> > > > @@ -187,11 +187,40 @@ extern "C" {
> > > >  /* add new RX flags here, don't forget to update PKT_FIRST_FREE */
> > > >
> > > >  #define PKT_FIRST_FREE (1ULL << 23)
> > > > -#define PKT_LAST_FREE (1ULL << 40)
> > > > +#define PKT_LAST_FREE (1ULL << 37)
> > > >
> > > >  /* add new TX flags here, don't forget to update PKT_LAST_FREE  */
> > > >
> > > >  /**
> > > > + * Packet marking offload flags. These flags indicated what kind
> > > > + * of packet marking needs to be applied on a given mbuf when
> > > > + * appropriate Traffic Manager configuration is in place.
> > > > + * When user set's these flags on a mbuf, below assumptions are made
> > > > + * 1) When PKT_TX_MARK_VLAN_DEI is set,
> > > > + * a) PMD assumes pkt to be a 802.1q packet.

What does that imply?

> > > > + * b) Application should also set mbuf.l2_len where 802.1Q header is
> > > > + *    at (mbuf.l2_len - 6) offset.

Why mbuf.l2_len - 6 ?

> > > > + * 2) When PKT_TX_MARK_IP_DSCP is set,
> > > > + * a) Application should also set either PKT_TX_IPV4 or PKT_TX_IPV6
> > > > + *    to indicate whether if it is IPv4 packet or IPv6 packet
> > > > + *    for DSCP marking. It should also set PKT_TX_IP_CKSUM if it is
> > > > + *    IPv4 pkt.
> > > > + * b) Application should also set mbuf.l2_len that indicates
> > > > + *    start offset of L3 header.
> > > > + * 3) When PKT_TX_MARK_IP_ECN is set,
> > > > + * a) Application should also set either PKT_TX_IPV4 or PKT_TX_IPV6.
> > > > + *    It should also set PKT_TX_IP_CKSUM if it is IPv4 pkt.
> > > > + * b) PMD will assume pkt L4 protocol is either TCP or SCTP and
> > > > + *    ECN is set to 2'b01 or 2'b10 as per RFC 3168 and hence HW
> > > > + *    can mark the packet for a configured color.
> > > > + * c) Application should also set mbuf.l2_len that indicates
> > > > + *    start offset of L3 header.
> > > > + */
> > > > +#define PKT_TX_MARK_VLAN_DEI           (1ULL << 38)
> > > > +#define PKT_TX_MARK_IP_DSCP            (1ULL << 39)
> > > > +#define PKT_TX_MARK_IP_ECN             (1ULL << 40)

We should have one comment per define.


> > > > +
> > > > +/**
> > > >   * Outer UDP checksum offload flag. This flag is used for enabling
> > > >   * outer UDP checksum in PMD. To use outer UDP checksum, the user needs to
> > > >   * 1) Enable the following in mbuf,
> > > > @@ -384,7 +413,10 @@ extern "C" {
> > > >                 PKT_TX_MACSEC |          \
> > > >                 PKT_TX_SEC_OFFLOAD |     \
> > > >                 PKT_TX_UDP_SEG |         \
> > > > -               PKT_TX_OUTER_UDP_CKSUM)
> > > > +               PKT_TX_OUTER_UDP_CKSUM | \
> > > > +               PKT_TX_MARK_VLAN_DEI |   \
> > > > +               PKT_TX_MARK_IP_DSCP |    \
> > > > +               PKT_TX_MARK_IP_ECN)
> > > >
> > > >  /**
> > > >   * Mbuf having an external buffer attached. shinfo in mbuf must be filled.
> > > > --
> > > > 2.8.4
> > > >