> -----Original Message-----
> From: Richardson, Bruce
> Sent: Friday, March 31, 2017 12:22 PM
> To: Olivier Matz <olivier.m...@6wind.com>
> Cc: dev@dpdk.org; Ananyev, Konstantin <konstantin.anan...@intel.com>;
> m...@smartsharesystems.com; Chilikin, Andrey
> <andrey.chili...@intel.com>; jblu...@infradead.org;
> nelio.laranje...@6wind.com; arybche...@solarflare.com
> Subject: Re: [PATCH 3/9] mbuf: set mbuf fields while in pool
>
> On Wed, Mar 08, 2017 at 10:41:55AM +0100, Olivier Matz wrote:
> > Set the value of m->refcnt to 1, m->nb_segs to 1 and m->next
> > to NULL when the mbuf is stored inside the mempool (unused).
> > This is done in rte_pktmbuf_prefree_seg(), before freeing or
> > recycling a mbuf.
> >
> > Before this patch, the value of m->refcnt was expected to be 0
> > while in pool.
> >
> > The objectives are:
> >
> > - to avoid drivers to set m->next to NULL in the early Rx path, since
> > this field is in the second 64B of the mbuf and its access could
> > trigger a cache miss
> >
> > - rationalize the behavior of raw_alloc/raw_free: one is now the
> > symmetric of the other, and refcnt is never changed in these functions.
> >
> > Signed-off-by: Olivier Matz <olivier.m...@6wind.com>
> > ---
> > drivers/net/mlx5/mlx5_rxtx.c | 5 ++---
> > drivers/net/mpipe/mpipe_tilegx.c | 1 +
> > lib/librte_mbuf/rte_mbuf.c | 2 ++
> > lib/librte_mbuf/rte_mbuf.h | 42
> > +++++++++++++++++++++++++++++-----------
> > 4 files changed, 36 insertions(+), 14 deletions(-)
> >
> <snip>
> > /**
> > @@ -1244,9 +1262,13 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > __rte_mbuf_sanity_check(m, 0);
> >
> > if (likely(rte_mbuf_refcnt_update(m, -1) == 0)) {
> > - /* if this is an indirect mbuf, it is detached. */
> > if (RTE_MBUF_INDIRECT(m))
> > rte_pktmbuf_detach(m);
> > +
> > + m->next = NULL;
> > + m->nb_segs = 1;
> > + rte_mbuf_refcnt_set(m, 1);
> > +
> > return m;
> > }
> > return NULL;
>
> Do we need to make this change to prefree_seg? If we update the detach
> function to set the next point to null on detaching a segment, and if we
> change the "free" function which frees a whole chain of mbufs, we should
> be covered, should we not? If we are freeing a standalone segment, that
> segment should already have it's nb_segs and next pointers correct.
detach() is invoked only for indirect mbufs.
We can have a chain of direct mbufs too.
About free() - most PMD use either rte_pktmbuf_free_seg()
or rte_pktmbuf_prefree_seg();rte_mempool_put_bulk(); directly.
Konstantin
