From: Joyce Kong <joyce.kong@arm.com>
Date: Mon, 21 Dec 2020 15:50:31 +0000 (+0800)
Subject: vhost: relax full barriers for used idx
X-Git-Url: http://git.droids-corp.org/?p=dpdk.git;a=commitdiff_plain;h=10b8c36af0abb654907d97738641d6a643408b99

vhost: relax full barriers for used idx

Used idx can be synchronized by one-way barrier instead of full
write barrier for split vring.

Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---

diff --git a/lib/librte_vhost/vdpa.c b/lib/librte_vhost/vdpa.c
index ae6fdd24ed..99a926a772 100644
--- a/lib/librte_vhost/vdpa.c
+++ b/lib/librte_vhost/vdpa.c
@@ -217,8 +217,8 @@ rte_vdpa_relay_vring_used(int vid, uint16_t qid, void *vring_m)
 		idx++;
 	}
 
-	rte_smp_wmb();
-	vq->used->idx = idx_m;
+	/* used idx is the synchronization point for the split vring */
+	__atomic_store_n(&vq->used->idx, idx_m, __ATOMIC_RELEASE);
 
 	if (dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX))
 		vring_used_event(s_vring) = idx_m;