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net/virtio: fix used index retrieved only once

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In the following loop:
    while (vq->vq_used_cons_idx != vq->vq_ring.used->idx) {
            ...
    }
There is no external function call or any explict memory barrier
in the loop, the re-read of used->idx might be optimized and only
be retrieved once.

Use of voaltile normally should be prohibited, and access_once
is Linux kernel's style to handle this issue; Once we have that
macro in DPDK, we could change to that style.

virtio_recv_mergable_pkts might also have the same issue, so fix
it as well.

Fixes: 823ad647950a ("virtio: support multiple queues")
Fixes: 13ce5e7eb94f ("virtio: mergeable buffers")

Signed-off-by: Huawei Xie <huawei.xie@intel.com>
Acked-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
This commit is contained in:
Huawei Xie 2016-06-20 01:48:52 +08:00 committed by Yuanhan Liu
parent 7e1eb993f2
commit b81026f1e7
3 changed files with 4 additions and 5 deletions
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4
drivers/net/virtio/virtio_ethdev.c
View File

@ -222,12 +222,12 @@ virtio_send_command(struct virtnet_ctl *cvq, struct virtio_pmd_ctrl *ctrl,
virtqueue_notify(vq);
rte_rmb();
while (vq->vq_used_cons_idx == vq->vq_ring.used->idx) {
while (VIRTQUEUE_NUSED(vq) == 0) {
rte_rmb();
usleep(100);
}
while (vq->vq_used_cons_idx != vq->vq_ring.used->idx) {
while (VIRTQUEUE_NUSED(vq)) {
uint32_t idx, desc_idx, used_idx;
struct vring_used_elem *uep;

2
drivers/net/virtio/virtio_ring.h
View File

@ -79,7 +79,7 @@ struct vring_used_elem {
struct vring_used {
uint16_t flags;
uint16_t idx;
volatile uint16_t idx;
struct vring_used_elem ring[0];
};

3
drivers/net/virtio/virtio_rxtx_simple.c
View File

@ -184,8 +184,7 @@ virtio_recv_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
if (unlikely(nb_pkts < RTE_VIRTIO_DESC_PER_LOOP))
return 0;
nb_used = *(volatile uint16_t *)&vq->vq_ring.used->idx -
vq->vq_used_cons_idx;
nb_used = VIRTQUEUE_NUSED(vq);
rte_compiler_barrier();