Re: [dpdk-dev] [PATCH v7 02/17] lib/ring: apis to support configurable element size

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>
> > > +
> > > +static __rte_always_inline void
> > > +enqueue_elems_128(struct rte_ring *r, uint32_t prod_head, const
> > > +void *obj_table, uint32_t n) { unsigned int i; const uint32_t size
> > > += r->size; uint32_t idx = prod_head & r->mask; __uint128_t *ring =
> > > +(__uint128_t *)&r[1]; const __uint128_t *obj = (const __uint128_t
> > > +*)obj_table; if (likely(idx + n < size)) { for (i = 0; i < (n &
> > > +~0x1); i += 2, idx += 2) { ring[idx] = obj[i]; ring[idx + 1] =
> > > +obj[i + 1];
> >
> >
> > AFAIK, that implies 16B aligned obj_table...
> > Would it always be the case?
> I am not sure from the compiler perspective.
> At least on Arm architecture, unaligned access (address that is accessed is not
> aligned to the size of the data element being accessed) will result in faults or
> require additional cycles. So, aligning on 16B should be fine.
Further, I would be changing this to use 'rte_int128_t' as '__uint128_t' is not defined on 32b systems.

> 
> >
> > > +}
> > > +switch (n & 0x1) {
> > > +case 1:
> > > +ring[idx++] = obj[i++];
> > > +}
> > > +} else {
> > > +for (i = 0; idx < size; i++, idx++) ring[idx] = obj[i];
> > > +/* Start at the beginning */
> > > +for (idx = 0; i < n; i++, idx++)
> > > +ring[idx] = obj[i];
> > > +}
> > > +}
> > > +
> > > +/* the actual enqueue of elements on the ring.
> > > + * Placed here since identical code needed in both
> > > + * single and multi producer enqueue functions.
> > > + */
> > > +static __rte_always_inline void
> > > +enqueue_elems(struct rte_ring *r, uint32_t prod_head, const void
> > *obj_table,
> > > +uint32_t esize, uint32_t num)
> > > +{
> > > +uint32_t idx, nr_idx, nr_num;
> > > +
> > > +/* 8B and 16B copies implemented individually to retain
> > > + * the current performance.
> > > + */
> > > +if (esize == 8)
> > > +enqueue_elems_64(r, prod_head, obj_table, num); else if (esize ==
> > > +16) enqueue_elems_128(r, prod_head, obj_table, num); else {
> > > +/* Normalize to uint32_t */
> > > +uint32_t scale = esize / sizeof(uint32_t); nr_num = num * scale;
> > > +idx = prod_head & r->mask; nr_idx = idx * scale;
> > > +enqueue_elems_32(r, nr_idx, obj_table, nr_num); } }
> > > +