On Wed, Mar 08, 2017 at 11:49:06AM +0100, Olivier MATZ wrote:
> On Thu, 23 Feb 2017 17:24:05 +0000, Bruce Richardson
> <bruce.richard...@intel.com> wrote:
> > We can write a single common function for head manipulation for enq
> > and a common one for deq, allowing us to have a single worker function
> > for enq and deq, rather than two of each. Update all other inline
> > functions to use the new functions.
> >
> > Signed-off-by: Bruce Richardson <bruce.richard...@intel.com>
> > ---
> > lib/librte_ring/rte_ring.c | 4 +-
> > lib/librte_ring/rte_ring.h | 328
> > ++++++++++++++++++++-------------------------
> > 2 files changed, 149 insertions(+), 183 deletions(-)
> >
>
> [...]
>
> > +static inline __attribute__((always_inline)) unsigned int
> > +__rte_ring_do_enqueue(struct rte_ring *r, void * const *obj_table,
> > + unsigned int n, enum rte_ring_queue_behavior behavior,
> > + int is_sp, unsigned int *free_space)
> > {
> > - uint32_t prod_head, cons_tail;
> > - uint32_t prod_next, free_entries;
> > - uint32_t mask = r->mask;
> > -
> > - prod_head = r->prod.head;
> > - cons_tail = r->cons.tail;
> > - /* The subtraction is done between two unsigned 32bits value
> > - * (the result is always modulo 32 bits even if we have
> > - * prod_head > cons_tail). So 'free_entries' is always between 0
> > - * and size(ring)-1. */
> > - free_entries = mask + cons_tail - prod_head;
> > -
> > - /* check that we have enough room in ring */
> > - if (unlikely(n > free_entries))
> > - n = (behavior == RTE_RING_QUEUE_FIXED) ? 0 : free_entries;
> > + uint32_t prod_head, prod_next;
> > + uint32_t free_entries;
> >
> > + n = __rte_ring_move_prod_head(r, is_sp, n, behavior,
> > + &prod_head, &prod_next, &free_entries);
> > if (n == 0)
> > goto end;
> >
> > -
> > - prod_next = prod_head + n;
> > - r->prod.head = prod_next;
> > -
> > - /* write entries in ring */
> > ENQUEUE_PTRS();
> > rte_smp_wmb();
> >
> > + /*
> > + * If there are other enqueues in progress that preceded us,
> > + * we need to wait for them to complete
> > + */
> > + while (unlikely(r->prod.tail != prod_head))
> > + rte_pause();
> > +
>
> I'd say this part should not be done in case is_sp == 1.
> Since it is sometimes a constant arg in an inline func, it may be better
> to add the if (is_sp == 0).
>
> [...]
>
Yes, it's an unnecessary check. However, having it in place for the sp
case made no performance difference in my test, so I decided to keep
the code shorter by avoiding an additional branch. If there is a
performance hit I'll remove it, but I would rather not add more branches
to the code in the absense of a real impact to not having them.
Regards,
/Bruce
