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. The flags started and dev_attached are consulted only inside update_queuing_status, where the per-queue handshake provides the real synchronization; their loads and stores are relaxed. Factor the per-queue allow_queuing store and while_queuing wait into a small update_queue() helper used by both rx and tx loops. Signed-off-by: Stephen Hemminger <[email protected]> --- drivers/net/vhost/rte_eth_vhost.c | 103 +++++++++++++++++++----------- 1 file changed, 65 insertions(+), 38 deletions(-) diff --git a/drivers/net/vhost/rte_eth_vhost.c b/drivers/net/vhost/rte_eth_vhost.c index 05940f2461..3b1eedfe42 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; @@ -86,14 +86,14 @@ struct vhost_queue { }; struct pmd_internal { - rte_atomic32_t dev_attached; + RTE_ATOMIC(uint32_t) dev_attached; char *iface_name; uint64_t flags; uint64_t disable_flags; uint64_t features; uint16_t max_queues; int vid; - rte_atomic32_t started; + RTE_ATOMIC(uint32_t) started; bool vlan_strip; bool rx_sw_csum; bool tx_sw_csum; @@ -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; } @@ -744,6 +758,19 @@ eth_vhost_unconfigure_intr(struct rte_eth_dev *eth_dev) } } +static inline void +update_queue(struct vhost_queue *vq, uint32_t allow, bool wait_queuing) +{ + /* seq_cst: pairs with the data-path's seq_cst store of + * while_queuing and seq_cst load of allow_queuing. See + * eth_vhost_rx(). + */ + rte_atomic_store_explicit(&vq->allow_queuing, allow, rte_memory_order_seq_cst); + if (wait_queuing) + rte_wait_until_equal_32((volatile uint32_t *)(uintptr_t)&vq->while_queuing, + 0, rte_memory_order_seq_cst); +} + static void update_queuing_status(struct rte_eth_dev *dev, bool wait_queuing) { @@ -751,14 +778,18 @@ update_queuing_status(struct rte_eth_dev *dev, bool wait_queuing) struct vhost_queue *vq; struct rte_vhost_vring_state *state; unsigned int i; - int allow_queuing = 1; + bool allow_queuing = true; if (!dev->data->rx_queues || !dev->data->tx_queues) return; - if (rte_atomic32_read(&internal->started) == 0 || - rte_atomic32_read(&internal->dev_attached) == 0) - allow_queuing = 0; + /* These are control-plane flags consulted only here; + * the real data-path handshake is on vq->allow_queuing below. + * Relaxed is sufficient. + */ + if (rte_atomic_load_explicit(&internal->started, rte_memory_order_relaxed) == 0 || + rte_atomic_load_explicit(&internal->dev_attached, rte_memory_order_relaxed) == 0) + allow_queuing = false; state = vring_states[dev->data->port_id]; @@ -767,24 +798,18 @@ 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_pause(); + + update_queue(vq, !!(allow_queuing && state->cur[vq->virtqueue_id]), + wait_queuing); } for (i = 0; i < dev->data->nb_tx_queues; i++) { 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_pause(); + + update_queue(vq, !!(allow_queuing && state->cur[vq->virtqueue_id]), + wait_queuing); } } @@ -848,7 +873,7 @@ new_device(int vid) } internal->vid = vid; - if (rte_atomic32_read(&internal->started) == 1) { + if (rte_atomic_load_explicit(&internal->started, rte_memory_order_relaxed) == 1) { queue_setup(eth_dev, internal); if (dev_conf->intr_conf.rxq) eth_vhost_configure_intr(eth_dev); @@ -863,7 +888,7 @@ new_device(int vid) vhost_dev_csum_configure(eth_dev); - rte_atomic32_set(&internal->dev_attached, 1); + rte_atomic_store_explicit(&internal->dev_attached, 1, rte_memory_order_relaxed); update_queuing_status(eth_dev, false); VHOST_LOG_LINE(INFO, "Vhost device %d created", vid); @@ -893,7 +918,7 @@ destroy_device(int vid) eth_dev = list->eth_dev; internal = eth_dev->data->dev_private; - rte_atomic32_set(&internal->dev_attached, 0); + rte_atomic_store_explicit(&internal->dev_attached, 0, rte_memory_order_relaxed); update_queuing_status(eth_dev, true); eth_vhost_unconfigure_intr(eth_dev); @@ -1148,11 +1173,11 @@ eth_dev_start(struct rte_eth_dev *eth_dev) } queue_setup(eth_dev, internal); - if (rte_atomic32_read(&internal->dev_attached) == 1 && + if (rte_atomic_load_explicit(&internal->dev_attached, rte_memory_order_relaxed) == 1 && dev_conf->intr_conf.rxq) eth_vhost_configure_intr(eth_dev); - rte_atomic32_set(&internal->started, 1); + rte_atomic_store_explicit(&internal->started, 1, rte_memory_order_relaxed); update_queuing_status(eth_dev, false); for (i = 0; i < eth_dev->data->nb_rx_queues; i++) @@ -1170,7 +1195,7 @@ eth_dev_stop(struct rte_eth_dev *dev) uint16_t i; dev->data->dev_started = 0; - rte_atomic32_set(&internal->started, 0); + rte_atomic_store_explicit(&internal->started, 0, rte_memory_order_relaxed); update_queuing_status(dev, true); for (i = 0; i < dev->data->nb_rx_queues; i++) @@ -1471,8 +1496,10 @@ vhost_dev_priv_dump(struct rte_eth_dev *dev, FILE *f) fprintf(f, "features: 0x%" PRIx64 "\n", internal->features); fprintf(f, "max_queues: %u\n", internal->max_queues); fprintf(f, "vid: %d\n", internal->vid); - fprintf(f, "started: %d\n", rte_atomic32_read(&internal->started)); - fprintf(f, "dev_attached: %d\n", rte_atomic32_read(&internal->dev_attached)); + fprintf(f, "started: %u\n", + rte_atomic_load_explicit(&internal->started, rte_memory_order_relaxed)); + fprintf(f, "dev_attached: %u\n", + rte_atomic_load_explicit(&internal->dev_attached, rte_memory_order_relaxed)); fprintf(f, "vlan_strip: %d\n", internal->vlan_strip); fprintf(f, "rx_sw_csum: %d\n", internal->rx_sw_csum); fprintf(f, "tx_sw_csum: %d\n", internal->tx_sw_csum); -- 2.53.0
