[dpdk-dev] [PATCH v2 1/2] service: add API to retrieve service core active

[Harry van Haaren <harry.van.haaren@intel.com>]

This commit adds a new experimental API which allows the user
to retrieve the active state of an lcore. Knowing when the service
lcore is completed its polling loop can be useful to applications
to avoid race conditions when e.g. finalizing statistics.

The service thread itself now has a variable to indicate if its
thread is active. When zero the service thread has completed its
service, and has returned from the service_runner_func() function.

Suggested-by: Lukasz Wojciechowski <l.wojciechow@partner.samsung.com>
Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>

---

Thanks for feedback Lukasz, please have a look and see if this was
what you were expecting?

Honnappa/Phil, are the __atomic_load/store's correct?

---
 lib/librte_eal/common/rte_service.c  | 14 ++++++++++++++
 lib/librte_eal/include/rte_service.h |  9 +++++++++
 lib/librte_eal/rte_eal_version.map   |  1 +
 3 files changed, 24 insertions(+)

diff --git a/lib/librte_eal/common/rte_service.c b/lib/librte_eal/common/rte_service.c
index 6a0e0ff65..4c276b006 100644
--- a/lib/librte_eal/common/rte_service.c
+++ b/lib/librte_eal/common/rte_service.c
@@ -65,6 +65,7 @@ struct core_state {
 	/* map of services IDs are run on this core */
 	uint64_t service_mask;
 	uint8_t runstate; /* running or stopped */
+	uint8_t thread_active; /* indicates when thread is in service_run() */
 	uint8_t is_service_core; /* set if core is currently a service core */
 	uint8_t service_active_on_lcore[RTE_SERVICE_NUM_MAX];
 	uint64_t loops;
@@ -457,6 +458,8 @@ service_runner_func(void *arg)
 	const int lcore = rte_lcore_id();
 	struct core_state *cs = &lcore_states[lcore];
 
+	__atomic_store_n(&cs->thread_active, 1, __ATOMIC_RELAXED);
+
 	/* runstate act as the guard variable. Use load-acquire
 	 * memory order here to synchronize with store-release
 	 * in runstate update functions.
@@ -475,9 +478,20 @@ service_runner_func(void *arg)
 		cs->loops++;
 	}
 
+	__atomic_store_n(&cs->thread_active, 0, __ATOMIC_RELAXED);
 	return 0;
 }
 
+int32_t
+rte_service_lcore_active(uint32_t lcore)
+{
+	if (lcore >= RTE_MAX_LCORE || !lcore_states[lcore].is_service_core)
+		return -EINVAL;
+
+	return __atomic_load_n(&lcore_states[lcore].thread_active,
+			       __ATOMIC_RELAXED);
+}
+
 int32_t
 rte_service_lcore_count(void)
 {
diff --git a/lib/librte_eal/include/rte_service.h b/lib/librte_eal/include/rte_service.h
index e2d0a6dd3..f7134b5c0 100644
--- a/lib/librte_eal/include/rte_service.h
+++ b/lib/librte_eal/include/rte_service.h
@@ -261,6 +261,15 @@ int32_t rte_service_lcore_start(uint32_t lcore_id);
  */
 int32_t rte_service_lcore_stop(uint32_t lcore_id);
 
+/**
+ * Reports if a service lcore is currently running.
+ * @retval 0 Service thread is not active, and has been returned to EAL.
+ * @retval 1 Service thread is in the service core polling loop.
+ * @retval -EINVAL Invalid *lcore_id* provided.
+ */
+__rte_experimental
+int32_t rte_service_lcore_active(uint32_t lcore_id);
+
 /**
  * Adds lcore to the list of service cores.
  *
diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
index bf0c17c23..d53d5d5b9 100644
--- a/lib/librte_eal/rte_eal_version.map
+++ b/lib/librte_eal/rte_eal_version.map
@@ -401,6 +401,7 @@ EXPERIMENTAL {
 	rte_lcore_dump;
 	rte_lcore_iterate;
 	rte_mp_disable;
+	rte_service_lcore_active;
 	rte_thread_register;
 	rte_thread_unregister;
 };
-- 
2.17.1