From 3d2c6743f4e0958df3189c9e8e08e7d56f1e0df7 Mon Sep 17 00:00:00 2001
From: Damjan Marion <damarion@cisco.com>
Date: Fri, 14 May 2021 14:36:23 +0200
Subject: [PATCH] memif: remove barriers

Type: improvement
Change-Id: Idef30aee80b654ce424b6f1f1f730574ca68874c
Signed-off-by: Damjan Marion <damarion@cisco.com>
---
 src/plugins/memif/device.c | 36 ++++++++++++++++++++++--------------
 src/plugins/memif/node.c   | 19 +++++++++++--------
 2 files changed, 33 insertions(+), 22 deletions(-)

diff --git a/src/plugins/memif/device.c b/src/plugins/memif/device.c
index d6d4ae3780b..befc0b50eab 100644
--- a/src/plugins/memif/device.c
+++ b/src/plugins/memif/device.c
@@ -112,6 +112,7 @@ memif_interface_tx_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
   memif_copy_op_t *co;
   memif_region_index_t last_region = ~0;
   void *last_region_shm = 0;
+  u16 head, tail;
 
   ring = mq->ring;
   ring_size = 1 << mq->log2_ring_size;
@@ -119,14 +120,20 @@ memif_interface_tx_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
 
 retry:
 
-  free_slots = ring->tail - mq->last_tail;
-  mq->last_tail += free_slots;
-  slot = (type == MEMIF_RING_S2M) ? ring->head : ring->tail;
-
   if (type == MEMIF_RING_S2M)
-    free_slots = ring_size - ring->head + mq->last_tail;
+    {
+      slot = head = ring->head;
+      tail = __atomic_load_n (&ring->tail, __ATOMIC_ACQUIRE);
+      mq->last_tail += tail - mq->last_tail;
+      free_slots = ring_size - head + mq->last_tail;
+    }
   else
-    free_slots = ring->head - ring->tail;
+    {
+      slot = tail = ring->tail;
+      head = __atomic_load_n (&ring->head, __ATOMIC_ACQUIRE);
+      mq->last_tail += tail - mq->last_tail;
+      free_slots = head - tail;
+    }
 
   while (n_left && free_slots)
     {
@@ -263,11 +270,10 @@ no_free_slots:
   vec_reset_length (ptd->copy_ops);
   vec_reset_length (ptd->buffers);
 
-  CLIB_MEMORY_STORE_BARRIER ();
   if (type == MEMIF_RING_S2M)
-    ring->head = slot;
+    __atomic_store_n (&ring->head, slot, __ATOMIC_RELEASE);
   else
-    ring->tail = slot;
+    __atomic_store_n (&ring->tail, slot, __ATOMIC_RELEASE);
 
   if (n_left && n_retries--)
     goto retry;
@@ -306,9 +312,13 @@ memif_interface_tx_zc_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
   u16 mask = ring_size - 1;
   int n_retries = 5;
   vlib_buffer_t *b0;
+  u16 head, tail;
 
 retry:
-  n_free = ring->tail - mq->last_tail;
+  slot = tail = __atomic_load_n (&ring->tail, __ATOMIC_ACQUIRE);
+  head = ring->head;
+
+  n_free = tail - mq->last_tail;
   if (n_free >= 16)
     {
       vlib_buffer_free_from_ring_no_next (vm, mq->buffers,
@@ -317,8 +327,7 @@ retry:
       mq->last_tail += n_free;
     }
 
-  slot = ring->head;
-  free_slots = ring_size - ring->head + mq->last_tail;
+  free_slots = ring_size - head + mq->last_tail;
 
   while (n_left && free_slots)
     {
@@ -375,8 +384,7 @@ retry:
     }
 no_free_slots:
 
-  CLIB_MEMORY_STORE_BARRIER ();
-  ring->head = slot;
+  __atomic_store_n (&ring->head, slot, __ATOMIC_RELEASE);
 
   if (n_left && n_retries--)
     goto retry;
diff --git a/src/plugins/memif/node.c b/src/plugins/memif/node.c
index 7c4de8b8564..24e8522636e 100644
--- a/src/plugins/memif/node.c
+++ b/src/plugins/memif/node.c
@@ -212,7 +212,12 @@ memif_device_input_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
   /* for S2M rings, we are consumers of packet buffers, and for M2S rings we
      are producers of empty buffers */
   cur_slot = (type == MEMIF_RING_S2M) ? mq->last_head : mq->last_tail;
-  last_slot = (type == MEMIF_RING_S2M) ? ring->head : ring->tail;
+
+  if (type == MEMIF_RING_S2M)
+    last_slot = __atomic_load_n (&ring->head, __ATOMIC_ACQUIRE);
+  else
+    last_slot = __atomic_load_n (&ring->tail, __ATOMIC_ACQUIRE);
+
   if (cur_slot == last_slot)
     goto refill;
   n_slots = last_slot - cur_slot;
@@ -336,8 +341,8 @@ memif_device_input_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
   /* release slots from the ring */
   if (type == MEMIF_RING_S2M)
     {
-      CLIB_MEMORY_STORE_BARRIER ();
-      ring->tail = mq->last_head = cur_slot;
+      __atomic_store_n (&ring->tail, cur_slot, __ATOMIC_RELEASE);
+      mq->last_head = cur_slot;
     }
   else
     {
@@ -537,8 +542,7 @@ refill:
 	  d->length = mif->run.buffer_size;
 	}
 
-      CLIB_MEMORY_STORE_BARRIER ();
-      ring->head = head;
+      __atomic_store_n (&ring->head, head, __ATOMIC_RELEASE);
     }
 
   return n_rx_packets;
@@ -583,7 +587,7 @@ memif_device_input_zc_inline (vlib_main_t * vm, vlib_node_runtime_t * node,
   buffer_length = vlib_buffer_get_default_data_size (vm) - start_offset;
 
   cur_slot = mq->last_tail;
-  last_slot = ring->tail;
+  last_slot = __atomic_load_n (&ring->tail, __ATOMIC_ACQUIRE);
   if (cur_slot == last_slot)
     goto refill;
   n_slots = last_slot - cur_slot;
@@ -867,8 +871,7 @@ refill:
       n_alloc -= 1;
     }
 
-  CLIB_MEMORY_STORE_BARRIER ();
-  ring->head = head;
+  __atomic_store_n (&ring->head, head, __ATOMIC_RELEASE);
 
 done:
   return n_rx_packets;
-- 
2.16.6