Re: [dpdk-dev] [patch v3] doc: announce API change in ethdev offload flags

[Jerin Jacob Kollanukkaran <jerinj@marvell.com>]

> -----Original Message-----
> From: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> Sent: Thursday, August 8, 2019 4:04 PM
> To: Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Pavan Nikhilesh
> Bhagavatula <pbhagavatula@marvell.com>; stephen@networkplumber.org;
> arybchenko@solarflare.com; hemant.agrawal@nxp.com;
> thomas@monjalon.net; Yigit, Ferruh <ferruh.yigit@intel.com>; Richardson,
> Bruce <bruce.richardson@intel.com>; Neil Horman
> <nhorman@tuxdriver.com>; Mcnamara, John <john.mcnamara@intel.com>;
> Kovacevic, Marko <marko.kovacevic@intel.com>
> Cc: dev@dpdk.org
> Subject: [EXT] RE: [dpdk-dev] [patch v3] doc: announce API change in ethdev
> offload flags
> 
> External Email
> 
> ----------------------------------------------------------------------
> 
> 
> > -----Original Message-----
> > From: Jerin Jacob Kollanukkaran [mailto:jerinj@marvell.com]
> > Sent: Thursday, August 8, 2019 11:23 AM
> > To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Pavan
> > Nikhilesh Bhagavatula <pbhagavatula@marvell.com>;
> > stephen@networkplumber.org; arybchenko@solarflare.com;
> > hemant.agrawal@nxp.com; thomas@monjalon.net; Yigit, Ferruh
> > <ferruh.yigit@intel.com>; Richardson, Bruce
> > <bruce.richardson@intel.com>; Neil Horman <nhorman@tuxdriver.com>;
> > Mcnamara, John <john.mcnamara@intel.com>; Kovacevic, Marko
> > <marko.kovacevic@intel.com>
> > Cc: dev@dpdk.org
> > Subject: RE: [dpdk-dev] [patch v3] doc: announce API change in ethdev
> > offload flags
> >
> > > -----Original Message-----
> > > From: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> > > Sent: Thursday, August 8, 2019 3:39 PM
> > > To: Jerin Jacob Kollanukkaran <jerinj@marvell.com>; Pavan Nikhilesh
> > > Bhagavatula <pbhagavatula@marvell.com>;
> stephen@networkplumber.org;
> > > arybchenko@solarflare.com; hemant.agrawal@nxp.com;
> > > thomas@monjalon.net; Yigit, Ferruh <ferruh.yigit@intel.com>;
> > > Richardson, Bruce <bruce.richardson@intel.com>; Neil Horman
> > > <nhorman@tuxdriver.com>; Mcnamara, John
> <john.mcnamara@intel.com>;
> > > Kovacevic, Marko <marko.kovacevic@intel.com>
> > > Cc: dev@dpdk.org
> > > Subject: [EXT] RE: [dpdk-dev] [patch v3] doc: announce API change in
> > > ethdev offload flags
> > >
> > > External Email
> > >
> > > --------------------------------------------------------------------
> > > --
> > > Hi Jerin,
> >
> > Hi Konstantin,
> >
> >
> > >
> > > > >
> > > > > Hi guys,
> > > > >
> > > > > >
> > > > > > From: Pavan Nikhilesh <pbhagavatula@marvell.com>
> > > > > >
> > > > > > Add new offload flags ``DEV_RX_OFFLOAD_PTYPE``,
> > > > > ``DEV_RX_OFFLOAD_RSS``
> > > > > > and ``DEV_RX_OFFLOAD_FLOW_MARK``.
> > > > > >
> > > > > > Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
> > > > > > Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
> > > > > > Acked-by: Jerin Jacob <jerinj@marvell.com>
> > > > > > ---
> > > > > >  v3 Changes:
> > > > > >  - DEV_RX_OFFLOAD_RSS -> DEV_RX_OFFLOAD_RSS_HASH
> (anndrew).
> > > > > >
> > > > > >  v2 Changes:
> > > > > >  - Reword for clarity.
> > > > > >
> > > > > >  doc/guides/rel_notes/deprecation.rst | 13 +++++++++++++
> > > > > >  1 file changed, 13 insertions(+)
> > > > > >
> > > > > > diff --git a/doc/guides/rel_notes/deprecation.rst
> > > > > > b/doc/guides/rel_notes/deprecation.rst
> > > > > > index 37b8592b6..056c5709f 100644
> > > > > > --- a/doc/guides/rel_notes/deprecation.rst
> > > > > > +++ b/doc/guides/rel_notes/deprecation.rst
> > > > > > @@ -78,3 +78,16 @@ Deprecation Notices
> > > > > >    to set new power environment if power environment was
> > > > > > already
> > > > > initialized.
> > > > > >    In this case the function will return -1 unless the
> > > > > > environment is unset
> > > > > first
> > > > > >    (using ``rte_power_unset_env``). Other function usage
> > > > > > scenarios will not
> > > > > change.
> > > > > > +
> > > > > > +* ethdev: New offload flags ``DEV_RX_OFFLOAD_PTYPE``,
> > > > > > +``DEV_RX_OFFLOAD_RSS_HASH``
> > > > > > +  and ``DEV_RX_OFFLOAD_FLOW_MARK`` will be added in 19.11.
> > > > >
> > > > > One question about DEV_RX_OFFLOAD_PTYPE:
> > > > > Does it mean that new ol_flags value (PKT_RX_PTYPE) will be
> > > > > introduced to indicate that mbuf.packet_type value is set?
> > > > > Or PMD will have to set  mbuf.packet_type to zero, when
> > > > > DEV_RX_OFFLOAD_PTYPE was not enabled by user?
> > > >
> > > > I was thinking when DEV_RX_OFFLOAD_PTYPE is set
> > > > - mbuf.packet_type will be valid and mbuf.packet_type will have
> > > > parsed
> > > packet type.
> > > > If not set
> > > > - mbuf.packet_type can be anything application should not use
> > > mbuf.packet_type field.
> > >
> > > But in that case, we do need a new value for ol_flags, PKT_RX_PTYPE
> > > or so, right?
> >
> > Since application has two knobs rte_eth_dev_get_supported_ptypes() and
> > DEV_RX_OFFLOAD_PTYPE. We may not need to new ol_flags for this
> change. Right?
> > i.e if application sets the DEV_RX_OFFLOAD_PTYPE, The application will
> > get the parsed ptypes by the driver(=
> rte_eth_dev_get_supported_ptypes()).
> > So there is no scope ambiguity. Right?
> 
> I still think there is:
> Imagine user has 2 eth devices, one does support DEV_RX_OFFLOAD_PTYPE,
> second doesn't.  Now he has a mix of packets from both devices, that you
> want t process.
> How would he figure out for which of them ptype values are valid, and for
> each are not?
> Trace back from what port he has received them?
> Not very convenient, and not always possible.

I thought so. But in that case, application can always set DEV_RX_OFFLOAD_PTYPE
Flags for all the ethdev ports. Right? Rather having any complicated ol_flags
or port based parsing. If limit the _contract_ to following, we are good. Right?
# when DEV_RX_OFFLOAD_PTYPE is set, mbuf.packet_type will be valid
and mbuf.packet_type will have parsed packet type

or the negative offload(This contract is pretty clear, I don't think any ambiguity at all)
# when DEV_RX_OFFLOAD_NO_PTYPE(something similar) is set,
mbuf.packet_type will be invalid. 

> I think we need either to introduce new ol_flag value (as we usually do for
> other RX offloads),
> or force PMD to always set ptype value.

Setting new  ol_flag value may effect performance for existing drivers
which don't planning to use this offload and it complicates the 
application to have additional check based on ol_flag. If you see any corner case with above section,

How about just setting as ptype as 0 incase it is not parsed by driver.
Actual lookup is the costly one, writing 0 to pytpe is not costly
as there are plenty of writes in Rx and it will be write merged(No CPU stall)

I did not get the complete picture of "rte_eth_dev_set_supported_ptypes(uint16_t port_id, uint32_t
ptype_mask); instead of DEV_RX_OFFLOAD_PTYPE? scheme", Does it help?

> Konstantin
> 
> >
> >
> > >
> > > >
> > > > This will avoid writes 0 to mbuf.packet_type and packet_type
> > > > parsing if
> > > offload is not set.
> > > >
> > > >
> > > > > If so, what is the advantage?
> > > > > Again in that case, would it be more plausible to introduce something
> like:
> > > > > rte_eth_dev_set_supported_ptypes(uint16_t port_id, uint32_t
> > > > > ptype_mask); instead of DEV_RX_OFFLOAD_PTYPE?
> > > >
> > > > Any scheme is fine where we can skip the  write 0 to
> > > > mbuf.packet_type and packet_type parsing If application is NOT
> interested in packet_type.
> > > >
> > > > > Konstantin
> > > > >
> > > > > > +  This will allow application to enable or disable PMDs from
> > > > > > + updating ``rte_mbuf`` fields ``rte_mbuf::packet_type``,
> > > > > > + ``rte_mbuf::hash::rss`` and  ``rte_mbuf::hash::fdir`` respectively.
> > > > > > +  This scheme will allow PMDs to avoid writes to ``rte_mbuf``
> > > > > > + fields on Rx and  thereby improve Rx performance if
> > > > > > + application
> > > wishes do so.
> > > > > > +  In 19.11 PMDs will still update the fields even when the
> > > > > > + offloads are not  enabled.
> > > > > > +  The exact semantics of the flags will be worked out later
> > > > > > + either by making  them negative offloads to avoid
> > > > > > + application change or positive offload to  align with
> > > > > > + existing offload flag
> > > semantics.
> > > > > > --
> > > > > > 2.17.1