[dpdk-dev] [PATCH 7/7] eal: add lcore hotplug notifications

[David Marchand]

Now that lcores can be dynamically allocated/freed, we will have to
notify DPDK components and applications of such events for cases where
per lcore context must be allocated/initialised.

Signed-off-by: David Marchand <david.marchand at redhat.com>
---
 lib/librte_eal/common/eal_common_lcore.c  | 91 +++++++++++++++++++++++
 lib/librte_eal/common/eal_common_thread.c | 11 ++-
 lib/librte_eal/common/eal_private.h       | 26 +++++++
 lib/librte_eal/include/rte_lcore.h        | 49 ++++++++++++
 lib/librte_eal/rte_eal_version.map        |  2 +
 5 files changed, 178 insertions(+), 1 deletion(-)

diff --git a/lib/librte_eal/common/eal_common_lcore.c b/lib/librte_eal/common/eal_common_lcore.c
index 6aca1b2fee..3a997d8115 100644
--- a/lib/librte_eal/common/eal_common_lcore.c
+++ b/lib/librte_eal/common/eal_common_lcore.c
@@ -212,6 +212,47 @@ rte_socket_id_by_idx(unsigned int idx)
 	return config->numa_nodes[idx];
 }
 
+struct lcore_notifier {
+	TAILQ_ENTRY(lcore_notifier) next;
+	rte_lcore_notifier_cb cb;
+	void *arg;
+};
+static TAILQ_HEAD(lcore_notifiers_head, lcore_notifier) lcore_notifiers =
+	TAILQ_HEAD_INITIALIZER(lcore_notifiers);
+static rte_spinlock_t lcore_notifiers_lock = RTE_SPINLOCK_INITIALIZER;
+
+void *
+rte_lcore_notifier_register(rte_lcore_notifier_cb cb, void *arg)
+{
+	struct lcore_notifier *notifier;
+
+	if (cb == NULL)
+		return NULL;
+
+	notifier = calloc(1, sizeof(*notifier));
+	if (notifier == NULL)
+		return NULL;
+
+	notifier->cb = cb;
+	notifier->arg = arg;
+	rte_spinlock_lock(&lcore_notifiers_lock);
+	TAILQ_INSERT_TAIL(&lcore_notifiers, notifier, next);
+	rte_spinlock_unlock(&lcore_notifiers_lock);
+
+	return notifier;
+}
+
+void
+rte_lcore_notifier_unregister(void *handle)
+{
+	struct lcore_notifier *notifier = handle;
+
+	rte_spinlock_lock(&lcore_notifiers_lock);
+	TAILQ_REMOVE(&lcore_notifiers, notifier, next);
+	rte_spinlock_unlock(&lcore_notifiers_lock);
+	free(notifier);
+}
+
 rte_spinlock_t external_lcore_lock = RTE_SPINLOCK_INITIALIZER;
 
 unsigned int
@@ -277,3 +318,53 @@ rte_lcore_dump(FILE *f)
 	}
 	rte_spinlock_unlock(&external_lcore_lock);
 }
+
+int
+eal_lcore_external_notify_allocated(unsigned int lcore_id)
+{
+	struct lcore_notifier *notifier;
+	int ret = 0;
+
+	RTE_LOG(DEBUG, EAL, "New lcore %u.\n", lcore_id);
+	rte_spinlock_lock(&lcore_notifiers_lock);
+	TAILQ_FOREACH(notifier, &lcore_notifiers, next) {
+		if (notifier->cb(lcore_id, RTE_LCORE_EVENT_NEW_EXTERNAL,
+				notifier->arg) == 0)
+			continue;
+
+		/* Some notifier refused the new lcore, inform all notifiers
+		 * that acked it.
+		 */
+		RTE_LOG(DEBUG, EAL, "A lcore notifier refused new lcore %u.\n",
+			lcore_id);
+
+		notifier = TAILQ_PREV(notifier, lcore_notifiers_head, next);
+		while (notifier != NULL) {
+			notifier->cb(lcore_id,
+				RTE_LCORE_EVENT_RELEASE_EXTERNAL,
+				notifier->arg);
+			notifier = TAILQ_PREV(notifier, lcore_notifiers_head,
+				next);
+		}
+		ret = -1;
+		break;
+	}
+	rte_spinlock_unlock(&lcore_notifiers_lock);
+
+	return ret;
+}
+
+void
+eal_lcore_external_notify_removed(unsigned int lcore_id)
+{
+	struct lcore_notifier *notifier;
+
+	RTE_LOG(DEBUG, EAL, "Released lcore %u.\n", lcore_id);
+	rte_spinlock_lock(&lcore_notifiers_lock);
+	TAILQ_FOREACH_REVERSE(notifier, &lcore_notifiers, lcore_notifiers_head,
+			next) {
+		notifier->cb(lcore_id, RTE_LCORE_EVENT_RELEASE_EXTERNAL,
+			notifier->arg);
+	}
+	rte_spinlock_unlock(&lcore_notifiers_lock);
+}
diff --git a/lib/librte_eal/common/eal_common_thread.c b/lib/librte_eal/common/eal_common_thread.c
index a81b192ff3..f66d1ccaef 100644
--- a/lib/librte_eal/common/eal_common_thread.c
+++ b/lib/librte_eal/common/eal_common_thread.c
@@ -285,6 +285,12 @@ rte_thread_register(void)
 
 	rte_thread_init(lcore_id, &cpuset);
 
+	if (lcore_id != LCORE_ID_ANY &&
+			eal_lcore_external_notify_allocated(lcore_id) < 0) {
+		eal_lcore_external_release(lcore_id);
+		RTE_PER_LCORE(_lcore_id) = lcore_id = LCORE_ID_ANY;
+	}
+
 	RTE_LOG(DEBUG, EAL, "Registered thread as lcore %u.\n", lcore_id);
 	RTE_PER_LCORE(thread_registered) = true;
 }
@@ -298,8 +304,11 @@ rte_thread_unregister(void)
 		return;
 
 	lcore_id = RTE_PER_LCORE(_lcore_id);
-	if (lcore_id != LCORE_ID_ANY)
+	if (lcore_id != LCORE_ID_ANY) {
+		eal_lcore_external_notify_removed(lcore_id);
 		eal_lcore_external_release(lcore_id);
+		RTE_PER_LCORE(_lcore_id) = LCORE_ID_ANY;
+	}
 
 	rte_thread_uninit();
 
diff --git a/lib/librte_eal/common/eal_private.h b/lib/librte_eal/common/eal_private.h
index 8dd850f68a..649697c368 100644
--- a/lib/librte_eal/common/eal_private.h
+++ b/lib/librte_eal/common/eal_private.h
@@ -283,6 +283,21 @@ uint64_t get_tsc_freq_arch(void);
  */
 unsigned int eal_lcore_external_reserve(void);
 
+/**
+ * Evaluate all lcore notifiers with a RTE_LCORE_EVENT_NEW_EXTERNAL event for
+ * the passed lcore.
+ * If an error is returned by one of them, then this change is rolled back:
+ * all previous lcore notifiers that had acked the RTE_LCORE_EVENT_NEW_EXTERNAL
+ * event receive a RTE_LCORE_EVENT_RELEASE_EXTERNAL event for the passed lcore.
+ *
+ * @param lcore_id
+ *   The lcore to consider.
+ * @return
+ *   - 0 if all notifiers agreed on the new lcore
+ *   - -1 if one of them refused
+ */
+int eal_lcore_external_notify_allocated(unsigned int lcore_id);
+
 /**
  * Release an external lcore.
  *
@@ -291,6 +306,17 @@ unsigned int eal_lcore_external_reserve(void);
  */
 void eal_lcore_external_release(unsigned int lcore_id);
 
+/**
+ * Evaluate all lcore notifiers with a RTE_LCORE_EVENT_RELEASE_EXTERNAL event
+ * for the passed lcore.
+ * This function must be called with a lcore that successfully passed
+ * eal_lcore_external_notify_allocated().
+ *
+ * @param lcore_id
+ *   The lcore with role ROLE_EXTERNAL to release.
+ */
+void eal_lcore_external_notify_removed(unsigned int lcore_id);
+
 /**
  * Prepare physical memory mapping
  * i.e. hugepages on Linux and
diff --git a/lib/librte_eal/include/rte_lcore.h b/lib/librte_eal/include/rte_lcore.h
index 9cf34efef4..e0fec33d5a 100644
--- a/lib/librte_eal/include/rte_lcore.h
+++ b/lib/librte_eal/include/rte_lcore.h
@@ -238,6 +238,55 @@ __rte_experimental
 void
 rte_lcore_dump(FILE *f);
 
+enum rte_lcore_event_type {
+	RTE_LCORE_EVENT_NEW_EXTERNAL,
+	RTE_LCORE_EVENT_RELEASE_EXTERNAL,
+};
+
+/**
+ * Callback prototype for getting lcore events.
+ *
+ * @param lcore_id
+ *   The lcore to consider for this event.
+ * @param event
+ *   The type of event on the lcore.
+ * @param arg
+ *   An opaque pointer passed at notifier registration.
+ * @return
+ *   - -1 when refusing this event,
+ *   - 0 otherwise.
+ */
+typedef int (*rte_lcore_notifier_cb)(unsigned int lcore_id,
+	enum rte_lcore_event_type event, void *arg);
+
+/**
+ * Register a lcore notifier.
+ *
+ * @param cb
+ *   The callback invoked for each lcore event with the arg argument.
+ *   See rte_lcore_notifier_cb description.
+ * @param arg
+ *   An optional argument that gets passed to the callback when it gets
+ *   invoked.
+ * @return
+ *   On success, returns an opaque pointer for the created notifier.
+ *   NULL on failure.
+ */
+__rte_experimental
+void *
+rte_lcore_notifier_register(rte_lcore_notifier_cb cb, void *arg);
+
+/**
+ * Unregister a lcore notifier.
+ *
+ * @param handle
+ *   The handle pointer returned by a former successful call to
+ *   rte_lcore_notifier_register.
+ */
+__rte_experimental
+void
+rte_lcore_notifier_unregister(void *handle);
+
 /**
  * Set core affinity of the current thread.
  * Support both EAL and non-EAL thread and update TLS.
diff --git a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
index 6754d52543..1e6f2aaacc 100644
--- a/lib/librte_eal/rte_eal_version.map
+++ b/lib/librte_eal/rte_eal_version.map
@@ -396,6 +396,8 @@ EXPERIMENTAL {
 
 	# added in 20.08
 	rte_lcore_dump;
+	rte_lcore_notifier_register;
+	rte_lcore_notifier_unregister;
 	rte_thread_register;
 	rte_thread_unregister;
 };
-- 
2.23.0