[dpdk-dev] [RFC PATCH 20.02] mbuf: hint PMD not to inline packet

[Shahaf Shuler]

Tuesday, October 22, 2019 6:17 PM, Jerin Jacob:
> <viacheslavo at mellanox.com>
> Subject: Re: [dpdk-dev] [RFC PATCH 20.02] mbuf: hint PMD not to inline
> packet

[...]

> > > I think, pushing this logic to the application is bad idea. But if
> > > you are writing some custom application and the per packet-level you
> > > need to control then this flag may be the only way.
> >
> > Yes. This flag is for custom application who do unique acceleration (by doing
> Zero copy for compute/compression/encryption accelerators) on specific
> platforms.
> > Such application is fully aware to the platform and the location where the
> data resides hence it is very simple for it to know how to set this flag.
> 
> # if it is per packet, it will be an implicit requirement to add it mbuf.
> 
> If so,
> # Does it makes sense to add through dynamic mbuf? Maybe it is not worth it
> for a single bit.

You mean 
1. expose PMD cap for it
2. application enables it on dev offloads
3. PMD register bitfield to the dynamic mbuf flags (rte_mbuf_dynflag_register)
4. application register same flag to get the bit offset

It can be OK, if the community don't see common use for such flag. 


> 
> Since we have only 17 bits (40 - 23) remaining for Rx and Tx and it is custom
> application requirement, how about adding PKT_PMD_CUSTOM1 flags so
> that similar requirement by other PMDs can leverage the same bit for such
> custom applications.(We have a similar use case for smart NIC (not so make
> much sense for generic
> applications)  but needed for per packet)
> 
> >
> > Note, This flag is 0 by default - meaning no hint and generic application
> works same as today.
> 
> 
> 
> 
> 
> 
> >
> > >
> > >
> > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > >
> > > > > > To support a mixed traffic pattern (some buffers from local
> > > > > > DRAM, some buffers from other devices) with high BW, a hint
> > > > > > flag is introduced in the mbuf.
> > > > > > Application will hint the PMD whether or not it should try to
> > > > > > inline the given mbuf data buffer. PMD should do best effort
> > > > > > to act upon this request.
> > > > > >
> > > > > > Signed-off-by: Shahaf Shuler <shahafs at mellanox.com>
> > > > > > ---
> > > > > >  lib/librte_mbuf/rte_mbuf.h | 9 +++++++++
> > > > > >  1 file changed, 9 insertions(+)
> > > > > >
> > > > > > diff --git a/lib/librte_mbuf/rte_mbuf.h
> > > > > > b/lib/librte_mbuf/rte_mbuf.h index 98225ec80b..5934532b7f
> > > > > > 100644
> > > > > > --- a/lib/librte_mbuf/rte_mbuf.h
> > > > > > +++ b/lib/librte_mbuf/rte_mbuf.h
> > > > > > @@ -203,6 +203,15 @@ extern "C" {
> > > > > >  /* add new TX flags here */
> > > > > >
> > > > > >  /**
> > > > > > + * Hint to PMD to not inline the mbuf data buffer to device
> > > > > > + * rather let the device use its DMA engine to fetch the data
> > > > > > +with the
> > > > > > + * provided pointer.
> > > > > > + *
> > > > > > + * This flag is a only a hint. PMD should enforce it as best effort.
> > > > > > + */
> > > > > > +#define PKT_TX_DONT_INLINE_HINT (1ULL << 39)
> > > > > > +
> > > > > > +/**
> > > > > >   * Indicate that the metadata field in the mbuf is in use.
> > > > > >   */
> > > > > >  #define PKT_TX_METADATA        (1ULL << 40)
> > > > > > --
> > > > > > 2.12.0
> > > > > >