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[0/1] Minor mistake in ring (en|de)queueing

Message ID 20220103142201.475552-1-amo@semihalf.com (mailing list archive)
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Andrzej Ostruszka Jan. 3, 2022, 2:22 p.m. UTC 
  Hi all,

Recently I was going through the ring implementation and I believe I've
found a small mistake.  Not a functional error, just a slightly
suboptimal behaviour for the specific case when we want to enqueue
exactly the number of elements that we can before wrapping to the ring
beginning (the same goes for dequeueing).

Imagine we have a ring of size 16 depicted below with indexes underneath
and consumer/producer pointing as shown.

|  ******        |
 0123456789ABCDEF
   ^     ^
   c     p

Now if we try to enqueue 8 elements we will end up at the check:

	if (likely(idx + n < size)) {

where idx (=8) is a producer head and n=8.  We will fail this check
even though we have the case of 8 elements available without wrapping to
the beginning of the ring.

I hope I'm not completely off the base here :), if I'm not then the
subsequent patch attempts to fix this.

Wit regards
Andrzej Ostruszka

Andrzej Ostruszka (1):
  ring: fix off by 1 mistake

 lib/ring/rte_ring_elem_pvt.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)