[dpdk-stable] patch 'net/memif: relax load of ring head for M2S ring' has been queued to stable release 19.11.6

[luca.boccassi at gmail.com]

Hi,

FYI, your patch has been queued to stable release 19.11.6

Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
It will be pushed if I get no objections before 10/30/20. So please
shout if anyone has objections.

Also note that after the patch there's a diff of the upstream commit vs the
patch applied to the branch. This will indicate if there was any rebasing
needed to apply to the stable branch. If there were code changes for rebasing
(ie: not only metadata diffs), please double check that the rebase was
correctly done.

Thanks.

Luca Boccassi

---
>From bac91cd3440496b6692b8442941ff5d78f13ff54 Mon Sep 17 00:00:00 2001
From: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
Date: Mon, 28 Sep 2020 14:03:29 -0500
Subject: [PATCH] net/memif: relax load of ring head for M2S ring

[ upstream commit 562fc6ef142c706b15136b80070dec84bb641d8b ]

For M2S rings, ring->head is updated by the receiver and eth_memif_rx
function is called in the context of receiving thread. The loads in
the receiver do not need to synchronize with its own stores.

Fixes: a2aafb9aa651 ("net/memif: optimize with one-way barrier")

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
Reviewed-by: Phil Yang <phil.yang at arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang at arm.com>
Reviewed-by: Jakub Grajciar <jgrajcia at cisco.com>
---
 drivers/net/memif/rte_eth_memif.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/net/memif/rte_eth_memif.c b/drivers/net/memif/rte_eth_memif.c
index 3b377bc54c..26c06d9055 100644
--- a/drivers/net/memif/rte_eth_memif.c
+++ b/drivers/net/memif/rte_eth_memif.c
@@ -398,7 +398,11 @@ no_free_bufs:
 
 refill:
 	if (type == MEMIF_RING_M2S) {
-		head = __atomic_load_n(&ring->head, __ATOMIC_ACQUIRE);
+		/* ring->head is updated by the receiver and this function
+		 * is called in the context of receiver thread. The loads in
+		 * the receiver do not need to synchronize with its own stores.
+		 */
+		head = __atomic_load_n(&ring->head, __ATOMIC_RELAXED);
 		n_slots = ring_size - head + mq->last_tail;
 
 		while (n_slots--) {
-- 
2.20.1

---
  Diff of the applied patch vs upstream commit (please double-check if non-empty:
---
--- -	2020-10-28 10:35:17.002396335 +0000
+++ 0170-net-memif-relax-load-of-ring-head-for-M2S-ring.patch	2020-10-28 10:35:11.776834028 +0000
@@ -1,14 +1,15 @@
-From 562fc6ef142c706b15136b80070dec84bb641d8b Mon Sep 17 00:00:00 2001
+From bac91cd3440496b6692b8442941ff5d78f13ff54 Mon Sep 17 00:00:00 2001
 From: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
 Date: Mon, 28 Sep 2020 14:03:29 -0500
 Subject: [PATCH] net/memif: relax load of ring head for M2S ring
 
+[ upstream commit 562fc6ef142c706b15136b80070dec84bb641d8b ]
+
 For M2S rings, ring->head is updated by the receiver and eth_memif_rx
 function is called in the context of receiving thread. The loads in
 the receiver do not need to synchronize with its own stores.
 
 Fixes: a2aafb9aa651 ("net/memif: optimize with one-way barrier")
-Cc: stable at dpdk.org
 
 Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
 Reviewed-by: Phil Yang <phil.yang at arm.com>
@@ -19,10 +20,10 @@
  1 file changed, 5 insertions(+), 1 deletion(-)
 
 diff --git a/drivers/net/memif/rte_eth_memif.c b/drivers/net/memif/rte_eth_memif.c
-index b72e24932e..6deab098b5 100644
+index 3b377bc54c..26c06d9055 100644
 --- a/drivers/net/memif/rte_eth_memif.c
 +++ b/drivers/net/memif/rte_eth_memif.c
-@@ -410,7 +410,11 @@ no_free_bufs:
+@@ -398,7 +398,11 @@ no_free_bufs:
  
  refill:
  	if (type == MEMIF_RING_M2S) {