DPDK patches and discussions
 help / color / mirror / Atom feed
From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Andrzej Ostruszka <amo@semihalf.com>, "dev@dpdk.org" <dev@dpdk.org>
Cc: "upstream@semihalf.com" <upstream@semihalf.com>
Subject: RE: [PATCH 1/1] ring: fix off by 1 mistake
Date: Mon, 10 Jan 2022 15:09:50 +0000	[thread overview]
Message-ID: <DM6PR11MB44913118C4CFEF31054C70639A509@DM6PR11MB4491.namprd11.prod.outlook.com> (raw)
In-Reply-To: <20220103142201.475552-2-amo@semihalf.com>

> When enqueueing/dequeueing to/from the ring we try to optimize by manual
> loop unrolling.  The check for this optimization looks like:
> 
> 	if (likely(idx + n < size)) {
> 
> where 'idx' points to the first usable element (empty slot for enqueue,
> data for dequeue).  The correct comparison here should be '<=' instead
> of '<'.
> 
> This is not a functional error since we fall back to the loop with
> correct checks on indexes.  Just a minor suboptimal behaviour for the
> case when we want to enqueue/dequeue exactly the number of elements that
> we have in the ring before wrapping to its beginning.
> 
> Signed-off-by: Andrzej Ostruszka <amo@semihalf.com>
> ---
>  lib/ring/rte_ring_elem_pvt.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/lib/ring/rte_ring_elem_pvt.h b/lib/ring/rte_ring_elem_pvt.h
> index 275ec55393..83788c56e6 100644
> --- a/lib/ring/rte_ring_elem_pvt.h
> +++ b/lib/ring/rte_ring_elem_pvt.h
> @@ -17,7 +17,7 @@ __rte_ring_enqueue_elems_32(struct rte_ring *r, const uint32_t size,
>  	unsigned int i;
>  	uint32_t *ring = (uint32_t *)&r[1];
>  	const uint32_t *obj = (const uint32_t *)obj_table;
> -	if (likely(idx + n < size)) {
> +	if (likely(idx + n <= size)) {
>  		for (i = 0; i < (n & ~0x7); i += 8, idx += 8) {
>  			ring[idx] = obj[i];
>  			ring[idx + 1] = obj[i + 1];
> @@ -62,7 +62,7 @@ __rte_ring_enqueue_elems_64(struct rte_ring *r, uint32_t prod_head,
>  	uint32_t idx = prod_head & r->mask;
>  	uint64_t *ring = (uint64_t *)&r[1];
>  	const unaligned_uint64_t *obj = (const unaligned_uint64_t *)obj_table;
> -	if (likely(idx + n < size)) {
> +	if (likely(idx + n <= size)) {
>  		for (i = 0; i < (n & ~0x3); i += 4, idx += 4) {
>  			ring[idx] = obj[i];
>  			ring[idx + 1] = obj[i + 1];
> @@ -95,7 +95,7 @@ __rte_ring_enqueue_elems_128(struct rte_ring *r, uint32_t prod_head,
>  	uint32_t idx = prod_head & r->mask;
>  	rte_int128_t *ring = (rte_int128_t *)&r[1];
>  	const rte_int128_t *obj = (const rte_int128_t *)obj_table;
> -	if (likely(idx + n < size)) {
> +	if (likely(idx + n <= size)) {
>  		for (i = 0; i < (n & ~0x1); i += 2, idx += 2)
>  			memcpy((void *)(ring + idx),
>  				(const void *)(obj + i), 32);
> @@ -151,7 +151,7 @@ __rte_ring_dequeue_elems_32(struct rte_ring *r, const uint32_t size,
>  	unsigned int i;
>  	uint32_t *ring = (uint32_t *)&r[1];
>  	uint32_t *obj = (uint32_t *)obj_table;
> -	if (likely(idx + n < size)) {
> +	if (likely(idx + n <= size)) {
>  		for (i = 0; i < (n & ~0x7); i += 8, idx += 8) {
>  			obj[i] = ring[idx];
>  			obj[i + 1] = ring[idx + 1];
> @@ -196,7 +196,7 @@ __rte_ring_dequeue_elems_64(struct rte_ring *r, uint32_t prod_head,
>  	uint32_t idx = prod_head & r->mask;
>  	uint64_t *ring = (uint64_t *)&r[1];
>  	unaligned_uint64_t *obj = (unaligned_uint64_t *)obj_table;
> -	if (likely(idx + n < size)) {
> +	if (likely(idx + n <= size)) {
>  		for (i = 0; i < (n & ~0x3); i += 4, idx += 4) {
>  			obj[i] = ring[idx];
>  			obj[i + 1] = ring[idx + 1];
> @@ -229,7 +229,7 @@ __rte_ring_dequeue_elems_128(struct rte_ring *r, uint32_t prod_head,
>  	uint32_t idx = prod_head & r->mask;
>  	rte_int128_t *ring = (rte_int128_t *)&r[1];
>  	rte_int128_t *obj = (rte_int128_t *)obj_table;
> -	if (likely(idx + n < size)) {
> +	if (likely(idx + n <= size)) {
>  		for (i = 0; i < (n & ~0x1); i += 2, idx += 2)
>  			memcpy((void *)(obj + i), (void *)(ring + idx), 32);
>  		switch (n & 0x1) {
> --

Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

> 2.34.1.448.ga2b2bfdf31-goog


  parent reply	other threads:[~2022-01-10 15:09 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-03 14:22 [PATCH 0/1] Minor mistake in ring (en|de)queueing Andrzej Ostruszka
2022-01-03 14:22 ` [PATCH 1/1] ring: fix off by 1 mistake Andrzej Ostruszka
2022-01-03 14:56   ` Morten Brørup
2022-01-06 10:45   ` Olivier Matz
2022-01-10 15:09   ` Ananyev, Konstantin [this message]
2022-01-11 11:49     ` Andrzej Ostruszka
2022-01-11 11:37   ` [PATCH] ring: optimize corner case for enqueue/dequeue Andrzej Ostruszka
2022-01-11 12:00     ` Morten Brørup
2022-01-11 13:46       ` Andrzej Ostruszka
2022-01-11 13:53         ` Morten Brørup
2022-02-05 16:48     ` David Marchand

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=DM6PR11MB44913118C4CFEF31054C70639A509@DM6PR11MB4491.namprd11.prod.outlook.com \
    --to=konstantin.ananyev@intel.com \
    --cc=amo@semihalf.com \
    --cc=dev@dpdk.org \
    --cc=upstream@semihalf.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).