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From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Andrzej Ostruszka" <amo@semihalf.com>, <dev@dpdk.org>
Cc: "Olivier Matz" <olivier.matz@6wind.com>,
	"Konstantin Ananyev" <konstantin.ananyev@intel.com>
Subject: RE: [PATCH] ring: optimize corner case for enqueue/dequeue
Date: Tue, 11 Jan 2022 13:00:25 +0100	[thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D86DF5@smartserver.smartshare.dk> (raw)
In-Reply-To: <20220111113739.1104058-1-amo@semihalf.com>

> From: Andrzej Ostruszka [mailto:amo@semihalf.com]
> Sent: Tuesday, 11 January 2022 12.38
> 
> 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.
> 
> Fixes: cc4b218790f6 ("ring: support configurable element size")
> Fixes: 286bd05bf70d ("ring: optimisations")
> 
> Signed-off-by: Andrzej Ostruszka <amo@semihalf.com>
> Reviewed-by: Olivier Matz <olivier.matz@6wind.com>
> Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.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) {
> --
> 2.34.1.575.g55b058a8bb-goog
> 

Also this version of the patch:

Reviewed-by: Morten Brørup <mb@smartsharesystems.com>


  reply	other threads:[~2022-01-11 12:00 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
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 [this message]
2022-01-11 13:46       ` Andrzej Ostruszka
2022-01-11 13:53         ` Morten Brørup
2022-02-05 16:48     ` David Marchand

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