On Fri, Jan 11, 2019 at 02:17:04PM +0300, Andrew Rybchenko wrote:
> Olivier, David,
>
> could you take a look at naming suggested below and share your thoughts.
> My fear is that rte_mbuf_buf_addr() is too generic and true for direct mbuf
> only. That's why I'd like to highlight it in the function name.
>
I would tend to agree with that concern.
/Bruce
> Thanks,
> Andrew.
>
> On 1/11/19 2:03 PM, Yongseok Koh wrote:
> > On Fri, Jan 11, 2019 at 11:14:22AM +0300, Andrew Rybchenko wrote:
> > > On 1/10/19 9:35 PM, Yongseok Koh wrote:
> > > > This patch introduces two new functions - rte_mbuf_buf_addr() and
> > > > rte_mbuf_data_addr_default().
> > > >
> > > > rte_mbuf_buf_addr() reutrns the default buffer address of given mbuf
> > > > which
> > > > comes after mbuf structure and private data.
> > > >
> > > > rte_mbuf_data_addr_default() returns the default address of mbuf data
> > > > taking the headroom into account.
> > > >
> > > > Signed-off-by: Yongseok Koh <ys...@mellanox.com>
> > > > ---
> > > >
> > > > v3:
> > > > * rename functions
> > > >
> > > > v2:
> > > > * initial implementation
> > > >
> > > > lib/librte_mbuf/rte_mbuf.h | 43
> > > > ++++++++++++++++++++++++++++++++++++++++---
> > > > 1 file changed, 40 insertions(+), 3 deletions(-)
> > > >
> > > > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > > > index bc562dc8a9..486566fc28 100644
> > > > --- a/lib/librte_mbuf/rte_mbuf.h
> > > > +++ b/lib/librte_mbuf/rte_mbuf.h
> > > > @@ -788,8 +788,47 @@ rte_mbuf_from_indirect(struct rte_mbuf *mi)
> > > > }
> > > > /**
> > > > + * Return the default buffer address of the mbuf.
> > > > + *
> > > > + * @param mb
> > > > + * The pointer to the mbuf.
> > > > + * @param mp
> > > > + * The pointer to the mempool of the mbuf.
> > > > + * @return
> > > > + * The pointer of the mbuf buffer.
> > > > + */
> > > > +static inline char * __rte_experimental
> > > > +rte_mbuf_buf_addr(struct rte_mbuf *mb, struct rte_mempool *mp)
> > > struct rte_mbuf has pool member. So, I don't understand why mp
> > > argument is required. I guess there is a reason, but it should be
> > > explained in comments. I see motivation in rte_mbuf_to_baddr()
> > > description, but rte_mbuf_buf_add() does not explain it.
> > Well, I don't like to put same comment here and there but I'll add small
> > comment
> > here.
> >
> > > Also right now the function name looks like simple get accessor for
> > > buf_addr and I'd expect to seem one line implementation may be
> > > with extra debug checks: return mb->buf_addr.
> > This func is suggested by David and Olivier because same code is being
> > repeated
> > in multiple locations. This can be used to initialize a mbuf when
> > mb->buf_addr is
> > null. And second use-case (this is my use-case) is to get the buf_addr
> > without
> > accessing the mbuf struct when mempool of mbuf is known, e.g. Rx buffer
> > replenishment. It is definitely beneficial for performance, especially RISC
> > cores.
> >
> > > May be rte_mbuf_direct_buf_addr() ?
> > > If so, similar below rte_mbuf_direct_data_addr_default().
> > Regarding naming, people have different tastes. As it is acked by Olivier
> > and
> > David, I'll keep the names.
>
> > Thanks,
> > Yongseok
> >
> > > > +{
> > > > + char *buffer_addr;
> > > > +
> > > > + buffer_addr = (char *)mb + sizeof(*mb) +
> > > > rte_pktmbuf_priv_size(mp);
> > > > + return buffer_addr;
> > > > +}
> > > > +
> > > > +
> > > > +/**
> > > > + * Return the default address of the beginning of the mbuf data.
> > > > + *
> > > > + * @param mb
> > > > + * The pointer to the mbuf.
> > > > + * @return
> > > > + * The pointer of the beginning of the mbuf data.
> > > > + */
> > > > +static inline char * __rte_experimental
> > > > +rte_mbuf_data_addr_default(struct rte_mbuf *mb)
> > > > +{
> > > > + return rte_mbuf_buf_addr(mb, mb->pool) + RTE_PKTMBUF_HEADROOM;
> > > > +}
> > > > +
> > > > +/**
> > > > * Return the buffer address embedded in the given mbuf.
> > > > *
> > > > + * Note that accessing mempool pointer of a mbuf is expensive because
> > > > the
> > > > + * pointer is stored in the 2nd cache line of mbuf. If mempool is
> > > > known, it
> > > > + * is better not to reference the mempool pointer in mbuf but calling
> > > > + * rte_mbuf_buf_addr() would be more efficient.
> > > > + *
> > > > * @param md
> > > > * The pointer to the mbuf.
> > > > * @return
> > > > @@ -798,9 +837,7 @@ rte_mbuf_from_indirect(struct rte_mbuf *mi)
> > > > static inline char *
> > > > rte_mbuf_to_baddr(struct rte_mbuf *md)
> > > > {
> > > > - char *buffer_addr;
> > > > - buffer_addr = (char *)md + sizeof(*md) +
> > > > rte_pktmbuf_priv_size(md->pool);
> > > > - return buffer_addr;
> > > > + return rte_mbuf_buf_addr(md, md->pool);
> > > > }
> > > > /**
>
