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From: Phil Yang <phil.yang@arm.com>
To: jerinj@marvell.com, dev@dpdk.org
Cc: thomas@monjalon.net, erik.g.carrillo@intel.com,
	Honnappa.Nagarahalli@arm.com, drc@linux.vnet.ibm.com,
	Ruifeng.Wang@arm.com, Dharmik.Thakkar@arm.com, nd@arm.com,
	david.marchand@redhat.com, mdr@ashroe.eu, nhorman@tuxdriver.com,
	dodji@redhat.com, stable@dpdk.org
Subject: [dpdk-dev] [PATCH v4 4/4] eventdev: relax smp barriers with C11 atomics
Date: Tue,  7 Jul 2020 23:54:53 +0800	[thread overview]
Message-ID: <1594137293-22468-4-git-send-email-phil.yang@arm.com> (raw)
In-Reply-To: <1594137293-22468-1-git-send-email-phil.yang@arm.com>

The impl_opaque field is shared between the timer arm and cancel
operations. Meanwhile, the state flag acts as a guard variable to
make sure the update of impl_opaque is synchronized. The original
code uses rte_smp barriers to achieve that. This patch uses C11
atomics with an explicit one-way memory barrier instead of full
barriers rte_smp_w/rmb() to avoid the unnecessary barrier on aarch64.

Since compilers can generate the same instructions for volatile and
non-volatile variable in C11 __atomics built-ins, so remain the volatile
keyword in front of state enum to avoid the ABI break issue.

Cc: stable@dpdk.org

Signed-off-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
---
v4:
1. Fix typo.
2. Cc to stable release. (Honnappa)

v3:
Fix ABI issue: revert to 'volatile enum rte_event_timer_state type state'.

v2:
1. Removed implementation-specific opaque data cleanup code.
2. Replaced thread fence with atomic ACQURE/RELEASE ordering on state access.

 lib/librte_eventdev/rte_event_timer_adapter.c | 55 ++++++++++++++++++---------
 1 file changed, 37 insertions(+), 18 deletions(-)

diff --git a/lib/librte_eventdev/rte_event_timer_adapter.c b/lib/librte_eventdev/rte_event_timer_adapter.c
index aa01b4d..4c5e49e 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 list for this lcore is not in use. */
 	uint16_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_ACQUIRE);
+		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 opaque 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);
@@ -1166,9 +1182,12 @@ 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;
-
-		rte_smp_wmb();
+		/* The RELEASE ordering here pairs with atomic ordering
+		 * to make sure the state update data observed between
+		 * threads.
+		 */
+		__atomic_store_n(&evtims[i]->state, RTE_EVENT_TIMER_CANCELED,
+				__ATOMIC_RELEASE);
 	}
 
 	return i;
-- 
2.7.4


  parent reply	other threads:[~2020-07-07 15:55 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-12 11:19 [dpdk-dev] [PATCH 1/3] eventdev: fix race condition on timer list counter Phil Yang
2020-06-12 11:19 ` [dpdk-dev] [PATCH 2/3] eventdev: use c11 atomics for lcore timer armed flag Phil Yang
2020-06-23 21:01   ` Carrillo, Erik G
2020-06-28 16:12     ` Phil Yang
2020-06-23 21:20   ` Stephen Hemminger
2020-06-23 21:31     ` Carrillo, Erik G
2020-06-28 16:32       ` Phil Yang
2020-06-12 11:19 ` [dpdk-dev] [PATCH 3/3] eventdev: relax smp barriers with c11 atomics Phil Yang
2020-06-22 10:12   ` Phil Yang
2020-06-23 19:38     ` Carrillo, Erik G
2020-06-28 17:33       ` Phil Yang
2020-06-29 18:07         ` Carrillo, Erik G
2020-06-18 15:17 ` [dpdk-dev] [PATCH 1/3] eventdev: fix race condition on timer list counter Carrillo, Erik G
2020-06-18 18:25   ` Honnappa Nagarahalli
2020-06-22  9:48     ` Phil Yang
2020-07-01 11:22       ` Jerin Jacob
2020-07-02  3:28         ` Phil Yang
2020-07-02  3:26     ` Phil Yang
2020-07-02  3:56       ` Honnappa Nagarahalli
2020-07-02 21:15         ` Carrillo, Erik G
2020-07-02 21:30           ` Honnappa Nagarahalli
2020-06-22  9:09   ` Phil Yang
2020-07-02  5:26 ` [dpdk-dev] [PATCH v2 1/4] " Phil Yang
2020-07-02  5:26   ` [dpdk-dev] [PATCH v2 2/4] eventdev: use c11 atomics for lcore timer armed flag Phil Yang
2020-07-02 20:21     ` Carrillo, Erik G
2020-07-02  5:26   ` [dpdk-dev] [PATCH v2 3/4] eventdev: remove redundant code Phil Yang
2020-07-03  3:35     ` Dharmik Thakkar
2020-07-02  5:26   ` [dpdk-dev] [PATCH v2 4/4] eventdev: relax smp barriers with c11 atomics Phil Yang
2020-07-02 20:30     ` Carrillo, Erik G
2020-07-03 10:50       ` Jerin Jacob
2020-07-06 10:04     ` Thomas Monjalon
2020-07-06 15:32       ` Phil Yang
2020-07-06 15:40         ` Thomas Monjalon
2020-07-07 11:13   ` [dpdk-dev] [PATCH v3 1/4] eventdev: fix race condition on timer list counter Phil Yang
2020-07-07 11:13     ` [dpdk-dev] [PATCH v3 2/4] eventdev: use C11 atomics for lcore timer armed flag Phil Yang
2020-07-07 11:13     ` [dpdk-dev] [PATCH v3 3/4] eventdev: remove redundant code Phil Yang
2020-07-07 11:13     ` [dpdk-dev] [PATCH v3 4/4] eventdev: relax smp barriers with C11 atomics Phil Yang
2020-07-07 14:29       ` Jerin Jacob
2020-07-07 15:56         ` Phil Yang
2020-07-07 15:54     ` [dpdk-dev] [PATCH v4 1/4] eventdev: fix race condition on timer list counter Phil Yang
2020-07-07 15:54       ` [dpdk-dev] [PATCH v4 2/4] eventdev: use C11 atomics for lcore timer armed flag Phil Yang
2020-07-07 15:54       ` [dpdk-dev] [PATCH v4 3/4] eventdev: remove redundant code Phil Yang
2020-07-07 15:54       ` Phil Yang [this message]
2020-07-08 13:30       ` [dpdk-dev] [PATCH v4 1/4] eventdev: fix race condition on timer list counter Jerin Jacob
2020-07-08 15:01         ` Thomas Monjalon

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