[dpdk-dev,v2] virtio: fix idx in used ring retrieved only once
Commit Message
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 would be optimized and would
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 have the same issue, so will be fixed.
Fixes: 823ad647950a ("virtio: support multiple queues")
Fixes: 13ce5e7eb94f ("virtio: mergeable buffers")
Signed-off-by: Huawei Xie <huawei.xie@intel.com>
---
v2: use VIRTQUEUE_NUSED
---
drivers/net/virtio/virtio_ethdev.c | 4 ++--
drivers/net/virtio/virtio_ring.h | 2 +-
drivers/net/virtio/virtio_rxtx_simple.c | 3 +--
3 files changed, 4 insertions(+), 5 deletions(-)
Comments
On Mon, Jun 20, 2016 at 01:48:52AM +0800, Huawei Xie wrote:
> 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 would be optimized and would
> 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 have the same issue, so will be fixed.
>
> Fixes: 823ad647950a ("virtio: support multiple queues")
> Fixes: 13ce5e7eb94f ("virtio: mergeable buffers")
>
> Signed-off-by: Huawei Xie <huawei.xie@intel.com>
Applied to dpdk-next-virtio.
Thanks.
--yliu
@@ -219,12 +219,12 @@ 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;
@@ -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];
};
@@ -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();