Convert allow_queuing, while_queuing, started, and dev_attached from rte_atomic32_t to RTE_ATOMIC(uint32_t) and replace rte_atomic32_*() with rte_atomic_*_explicit().
The data-path / control-thread handshake on allow_queuing and while_queuing is a Dekker-style mutual-visibility pattern: each side stores its own flag and then loads the peer's. Both legs must be seq_cst to forbid store-load reordering; anything weaker permits both sides to miss each other. The previous rte_atomic32_set/read compiled to plain volatile stores/loads and provided no such ordering, so this also closes a latent ordering hole on weakly-ordered ISAs. The data-path exit store of while_queuing=0 is release, ordering preceding slot accesses before the control thread observes the data path as idle. Signed-off-by: Stephen Hemminger <[email protected]> --- drivers/net/vhost/rte_eth_vhost.c | 62 ++++++++++++++++++++----------- 1 file changed, 40 insertions(+), 22 deletions(-) diff --git a/drivers/net/vhost/rte_eth_vhost.c b/drivers/net/vhost/rte_eth_vhost.c index 2e3a007966..2acf670c94 100644 --- a/drivers/net/vhost/rte_eth_vhost.c +++ b/drivers/net/vhost/rte_eth_vhost.c @@ -73,8 +73,8 @@ struct vhost_stats { struct vhost_queue { int vid; - rte_atomic32_t allow_queuing; - rte_atomic32_t while_queuing; + RTE_ATOMIC(uint32_t) allow_queuing; + RTE_ATOMIC(uint32_t) while_queuing; struct pmd_internal *internal; struct rte_mempool *mb_pool; uint16_t port; @@ -406,12 +406,19 @@ eth_vhost_rx(void *q, struct rte_mbuf **bufs, uint16_t nb_bufs) uint16_t i, nb_rx = 0; uint16_t nb_receive = nb_bufs; - if (unlikely(rte_atomic32_read(&r->allow_queuing) == 0)) + /* Fast-path early exit; racy load is fine here -- if we miss a + * transition we get caught by the seq_cst check below. + */ + if (unlikely(rte_atomic_load_explicit(&r->allow_queuing, rte_memory_order_relaxed) == 0)) return 0; - rte_atomic32_set(&r->while_queuing, 1); - - if (unlikely(rte_atomic32_read(&r->allow_queuing) == 0)) + /* Announce presence, then re-check. The store and the following + * load MUST both be seq_cst so they are totally ordered with the + * control thread's store-to-allow_queuing / load-of-while_queuing + * pair. Anything weaker permits both sides to miss each other. + */ + rte_atomic_store_explicit(&r->while_queuing, 1, rte_memory_order_seq_cst); + if (unlikely(rte_atomic_load_explicit(&r->allow_queuing, rte_memory_order_seq_cst) == 0)) goto out; /* Dequeue packets from guest TX queue */ @@ -446,7 +453,7 @@ eth_vhost_rx(void *q, struct rte_mbuf **bufs, uint16_t nb_bufs) } out: - rte_atomic32_set(&r->while_queuing, 0); + rte_atomic_store_explicit(&r->while_queuing, 0, rte_memory_order_release); return nb_rx; } @@ -460,12 +467,19 @@ eth_vhost_tx(void *q, struct rte_mbuf **bufs, uint16_t nb_bufs) uint64_t nb_bytes = 0; uint64_t nb_missed = 0; - if (unlikely(rte_atomic32_read(&r->allow_queuing) == 0)) + /* Fast-path early exit; racy load is fine here -- if we miss a + * transition we get caught by the seq_cst check below. + */ + if (unlikely(rte_atomic_load_explicit(&r->allow_queuing, rte_memory_order_relaxed) == 0)) return 0; - rte_atomic32_set(&r->while_queuing, 1); - - if (unlikely(rte_atomic32_read(&r->allow_queuing) == 0)) + /* Announce presence, then re-check. The store and the following + * load MUST both be seq_cst so they are totally ordered with the + * control thread's store-to-allow_queuing / load-of-while_queuing + * pair. Anything weaker permits both sides to miss each other. + */ + rte_atomic_store_explicit(&r->while_queuing, 1, rte_memory_order_seq_cst); + if (unlikely(rte_atomic_load_explicit(&r->allow_queuing, rte_memory_order_seq_cst) == 0)) goto out; for (i = 0; i < nb_bufs; i++) { @@ -515,7 +529,7 @@ eth_vhost_tx(void *q, struct rte_mbuf **bufs, uint16_t nb_bufs) for (i = 0; likely(i < nb_tx); i++) rte_pktmbuf_free(bufs[i]); out: - rte_atomic32_set(&r->while_queuing, 0); + rte_atomic_store_explicit(&r->while_queuing, 0, rte_memory_order_release); return nb_tx; } @@ -771,11 +785,13 @@ update_queuing_status(struct rte_eth_dev *dev, bool wait_queuing) vq = dev->data->rx_queues[i]; if (vq == NULL) continue; - if (allow_queuing && state->cur[vq->virtqueue_id]) - rte_atomic32_set(&vq->allow_queuing, 1); - else - rte_atomic32_set(&vq->allow_queuing, 0); - while (wait_queuing && rte_atomic32_read(&vq->while_queuing)) + + rte_atomic_store_explicit(&vq->allow_queuing, + (allow_queuing && state->cur[vq->virtqueue_id]), + rte_memory_order_seq_cst); + + while (wait_queuing && + rte_atomic_load_explicit(&vq->while_queuing, rte_memory_order_seq_cst)) rte_pause(); } @@ -783,11 +799,13 @@ update_queuing_status(struct rte_eth_dev *dev, bool wait_queuing) vq = dev->data->tx_queues[i]; if (vq == NULL) continue; - if (allow_queuing && state->cur[vq->virtqueue_id]) - rte_atomic32_set(&vq->allow_queuing, 1); - else - rte_atomic32_set(&vq->allow_queuing, 0); - while (wait_queuing && rte_atomic32_read(&vq->while_queuing)) + + rte_atomic_store_explicit(&vq->allow_queuing, + (allow_queuing && state->cur[vq->virtqueue_id]), + rte_memory_order_seq_cst); + + while (wait_queuing && + rte_atomic_load_explicit(&vq->while_queuing, rte_memory_order_seq_cst)) rte_pause(); } } -- 2.53.0
