[dpdk-dev] [PATCH 3/3] eventdev: relax smp barriers with c11 atomics
From: Phil Yang <hidden>
Date: 2020-06-12 11:20:50
Subsystem:
library code, the rest · Maintainers:
Andrew Morton, Linus Torvalds
The implementation-specific opaque data is shared between arm and cancel operations. The state flag acts as a guard variable to make sure the update of opaque data is synchronized. This patch uses c11 atomics with explicit one way memory barrier instead of full barriers rte_smp_w/rmb() to synchronize the opaque data between timer arm and cancel threads. Signed-off-by: Phil Yang <redacted> Reviewed-by: Dharmik Thakkar <redacted> Reviewed-by: Ruifeng Wang <redacted> --- lib/librte_eventdev/rte_event_timer_adapter.c | 55 ++++++++++++++++++--------- lib/librte_eventdev/rte_event_timer_adapter.h | 2 +- 2 files changed, 38 insertions(+), 19 deletions(-)
diff --git a/lib/librte_eventdev/rte_event_timer_adapter.c b/lib/librte_eventdev/rte_event_timer_adapter.c
index 6947efb..0a26501 100644
--- a/lib/librte_eventdev/rte_event_timer_adapter.c
+++ b/lib/librte_eventdev/rte_event_timer_adapter.c@@ -629,7 +629,8 @@ swtim_callback(struct rte_timer *tim) sw->expired_timers[sw->n_expired_timers++] = tim; sw->stats.evtim_exp_count++; - evtim->state = RTE_EVENT_TIMER_NOT_ARMED; + __atomic_store_n(&evtim->state, RTE_EVENT_TIMER_NOT_ARMED, + __ATOMIC_RELEASE); } if (event_buffer_batch_ready(&sw->buffer)) {
@@ -1020,6 +1021,7 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter, int n_lcores; /* Timer is not armed state */ int16_t exp_state = 0; + enum rte_event_timer_state n_state; #ifdef RTE_LIBRTE_EVENTDEV_DEBUG /* Check that the service is running. */
@@ -1060,30 +1062,36 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter, } for (i = 0; i < nb_evtims; i++) { - /* Don't modify the event timer state in these cases */ - if (evtims[i]->state == RTE_EVENT_TIMER_ARMED) { + n_state = __atomic_load_n(&evtims[i]->state, __ATOMIC_RELAXED); + if (n_state == RTE_EVENT_TIMER_ARMED) { rte_errno = EALREADY; break; - } else if (!(evtims[i]->state == RTE_EVENT_TIMER_NOT_ARMED || - evtims[i]->state == RTE_EVENT_TIMER_CANCELED)) { + } else if (!(n_state == RTE_EVENT_TIMER_NOT_ARMED || + n_state == RTE_EVENT_TIMER_CANCELED)) { rte_errno = EINVAL; break; } ret = check_timeout(evtims[i], adapter); if (unlikely(ret == -1)) { - evtims[i]->state = RTE_EVENT_TIMER_ERROR_TOOLATE; + __atomic_store_n(&evtims[i]->state, + RTE_EVENT_TIMER_ERROR_TOOLATE, + __ATOMIC_RELAXED); rte_errno = EINVAL; break; } else if (unlikely(ret == -2)) { - evtims[i]->state = RTE_EVENT_TIMER_ERROR_TOOEARLY; + __atomic_store_n(&evtims[i]->state, + RTE_EVENT_TIMER_ERROR_TOOEARLY, + __ATOMIC_RELAXED); rte_errno = EINVAL; break; } if (unlikely(check_destination_event_queue(evtims[i], adapter) < 0)) { - evtims[i]->state = RTE_EVENT_TIMER_ERROR; + __atomic_store_n(&evtims[i]->state, + RTE_EVENT_TIMER_ERROR, + __ATOMIC_RELAXED); rte_errno = EINVAL; break; }
@@ -1099,13 +1107,18 @@ __swtim_arm_burst(const struct rte_event_timer_adapter *adapter, SINGLE, lcore_id, NULL, evtims[i]); if (ret < 0) { /* tim was in RUNNING or CONFIG state */ - evtims[i]->state = RTE_EVENT_TIMER_ERROR; + __atomic_store_n(&evtims[i]->state, + RTE_EVENT_TIMER_ERROR, + __ATOMIC_RELEASE); break; } - rte_smp_wmb(); EVTIM_LOG_DBG("armed an event timer"); - evtims[i]->state = RTE_EVENT_TIMER_ARMED; + /* RELEASE ordering guarantees the adapter specific value + * changes observed before the update of state. + */ + __atomic_store_n(&evtims[i]->state, RTE_EVENT_TIMER_ARMED, + __ATOMIC_RELEASE); } if (i < nb_evtims)
@@ -1132,6 +1145,7 @@ swtim_cancel_burst(const struct rte_event_timer_adapter *adapter, struct rte_timer *timp; uint64_t opaque; struct swtim *sw = swtim_pmd_priv(adapter); + enum rte_event_timer_state n_state; #ifdef RTE_LIBRTE_EVENTDEV_DEBUG /* Check that the service is running. */
@@ -1143,16 +1157,18 @@ swtim_cancel_burst(const struct rte_event_timer_adapter *adapter, for (i = 0; i < nb_evtims; i++) { /* Don't modify the event timer state in these cases */ - if (evtims[i]->state == RTE_EVENT_TIMER_CANCELED) { + /* ACQUIRE ordering guarantees the access of implementation + * specific opague data under the correct state. + */ + n_state = __atomic_load_n(&evtims[i]->state, __ATOMIC_ACQUIRE); + if (n_state == RTE_EVENT_TIMER_CANCELED) { rte_errno = EALREADY; break; - } else if (evtims[i]->state != RTE_EVENT_TIMER_ARMED) { + } else if (n_state != RTE_EVENT_TIMER_ARMED) { rte_errno = EINVAL; break; } - rte_smp_rmb(); - opaque = evtims[i]->impl_opaque[0]; timp = (struct rte_timer *)(uintptr_t)opaque; RTE_ASSERT(timp != NULL);
@@ -1166,11 +1182,14 @@ swtim_cancel_burst(const struct rte_event_timer_adapter *adapter, rte_mempool_put(sw->tim_pool, (void **)timp); - evtims[i]->state = RTE_EVENT_TIMER_CANCELED; + __atomic_store_n(&evtims[i]->state, RTE_EVENT_TIMER_CANCELED, + __ATOMIC_RELAXED); evtims[i]->impl_opaque[0] = 0; evtims[i]->impl_opaque[1] = 0; - - rte_smp_wmb(); + /* The RELEASE fence make sure the clean up + * of opaque data observed between threads. + */ + __atomic_thread_fence(__ATOMIC_RELEASE); } return i;
diff --git a/lib/librte_eventdev/rte_event_timer_adapter.h b/lib/librte_eventdev/rte_event_timer_adapter.h
index d2ebcb0..6f64b90 100644
--- a/lib/librte_eventdev/rte_event_timer_adapter.h
+++ b/lib/librte_eventdev/rte_event_timer_adapter.h@@ -467,7 +467,7 @@ struct rte_event_timer { * - op: RTE_EVENT_OP_NEW * - event_type: RTE_EVENT_TYPE_TIMER */ - volatile enum rte_event_timer_state state; + enum rte_event_timer_state state; /**< State of the event timer. */ uint64_t timeout_ticks; /**< Expiry timer ticks expressed in number of *timer_ticks_ns* from
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2.7.4