On Wed, Sep 25, 2019 at 09:02:28PM +0200, Mattias Rönnblom wrote:
> On 2019-09-25 14:03, Morten Brørup wrote:
> > Add function for freeing a bulk of mbufs.
> >
> > Signed-off-by: Morten Brørup <m...@smartsharesystems.com>
> > ---
> > lib/librte_mbuf/rte_mbuf.c | 35 +++++++++++++++++++++++++++++++++++
> > lib/librte_mbuf/rte_mbuf.h | 16 +++++-----------
> > 2 files changed, 40 insertions(+), 11 deletions(-)
> >
> > diff --git a/lib/librte_mbuf/rte_mbuf.c b/lib/librte_mbuf/rte_mbuf.c
> > index 37718d49c..b63a0eced 100644
> > --- a/lib/librte_mbuf/rte_mbuf.c
> > +++ b/lib/librte_mbuf/rte_mbuf.c
> > @@ -245,6 +245,41 @@ int rte_mbuf_check(const struct rte_mbuf *m, int
> > is_header,
> > return 0;
> > }
> > +/**
> > + * Maximum bulk of mbufs rte_pktmbuf_free_bulk() returns to mempool.
> > + */
> > +#define RTE_PKTMBUF_FREE_BULK_SZ 64
> > +
> > +/* Free a bulk of mbufs back into their original mempools. */
> > +void rte_pktmbuf_free_bulk(struct rte_mbuf **mbufs, unsigned int count)
> > +{
> > + struct rte_mbuf *m, *free[RTE_PKTMBUF_FREE_BULK_SZ];
> > + unsigned int idx, nb_free = 0;
> > +
> > + for (idx = 0; idx < count; idx++) {
> > + m = mbufs[idx];
> > + if (unlikely(m == NULL))
> > + continue;
> > +
> > + __rte_mbuf_sanity_check(m, 1);
> > + m = rte_pktmbuf_prefree_seg(m);
> > + if (unlikely(m == NULL))
> > + continue;
> > +
> > + if (nb_free >= RTE_PKTMBUF_FREE_BULK_SZ ||
> > + (nb_free > 0 && m->pool != free[0]->pool)) {
>
> Maybe an unlikely() would be in order here?
>
I'd caution against it, since it can penalize the cold branch a lot. If a
branch really is predictable the HW branch predictors generally are good
enough to handle it at runtime. So long as a path is a valid path for a
runtime app, i.e. not something like a fatal error only ever hit once in an
entire run, I'd tend to omit likely()/unlikely() calls unless profiling
shows a real performance difference.
/Bruce
