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

[Jerin Jacob <jerinjacobk@gmail.com>]

On Wed, Oct 23, 2019 at 4:54 PM Shahaf Shuler <shahafs@mellanox.com> wrote:
>
> Tuesday, October 22, 2019 6:17 PM, Jerin Jacob:
> > <viacheslavo@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.

Any scheme based on dynamic mbuf flags should be fine.

>
>
> >
> > 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@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
> > > > > > >