service: fix race condition for MT unsafe service

A MT unsafe service might get configured to run on another core
while the service is running currently. This might result in the
MT unsafe service running on multiple cores simultaneously. Use
'execute_lock' always when the service is MT unsafe.

If the service is known to be mapped on a single lcore,
setting the service capability to MT safe will avoid taking
the lock and improve the performance.

Fixes: e9139a32f6e8 ("service: add function to run on app lcore")
Cc: stable@dpdk.org
Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>

diff --git a/lib/librte_eal/common/rte_service.c b/lib/librte_eal/common/rte_service.c
index 70d17a5..b8c465e 100644 (file)
--- a/lib/librte_eal/common/rte_service.c
+++ b/lib/librte_eal/common/rte_service.c
@@ -50,6 +50,10 @@ struct rte_service_spec_impl {
        uint8_t internal_flags;
 
        /* per service statistics */
+       /* Indicates how many cores the service is mapped to run on.
+        * It does not indicate the number of cores the service is running
+        * on currently.
+        */
        rte_atomic32_t num_mapped_cores;
        uint64_t calls;
        uint64_t cycles_spent;
@@ -370,12 +374,7 @@ service_run(uint32_t i, struct core_state *cs, uint64_t service_mask,
 
        cs->service_active_on_lcore[i] = 1;
 
-       /* check do we need cmpset, if MT safe or <= 1 core
-        * mapped, atomic ops are not required.
-        */
-       const int use_atomics = (service_mt_safe(s) == 0) &&
-                               (rte_atomic32_read(&s->num_mapped_cores) > 1);
-       if (use_atomics) {
+       if (service_mt_safe(s) == 0) {
                if (!rte_atomic32_cmpset((uint32_t *)&s->execute_lock, 0, 1))
                        return -EBUSY;
 

diff --git a/lib/librte_eal/include/rte_service.h b/lib/librte_eal/include/rte_service.h
index d8701dd..3a1c735 100644 (file)
--- a/lib/librte_eal/include/rte_service.h
+++ b/lib/librte_eal/include/rte_service.h
@@ -104,12 +104,16 @@ int32_t rte_service_probe_capability(uint32_t id, uint32_t capability);
  * Each core can be added or removed from running a specific service. This
  * function enables or disables *lcore* to run *service_id*.
  *
- * If multiple cores are enabled on a service, an atomic is used to ensure that
- * only one cores runs the service at a time. The exception to this is when
+ * If multiple cores are enabled on a service, a lock is used to ensure that
+ * only one core runs the service at a time. The exception to this is when
  * a service indicates that it is multi-thread safe by setting the capability
  * called RTE_SERVICE_CAP_MT_SAFE. With the multi-thread safe capability set,
  * the service function can be run on multiple threads at the same time.
  *
+ * If the service is known to be mapped to a single lcore, setting the
+ * capability of the service to RTE_SERVICE_CAP_MT_SAFE can achieve
+ * better performance by avoiding the use of lock.
+ *
  * @param service_id the service to apply the lcore to
  * @param lcore The lcore that will be mapped to service
  * @param enable Zero to unmap or disable the core, non-zero to enable

diff --git a/lib/librte_eal/include/rte_service_component.h b/lib/librte_eal/include/rte_service_component.h
index 16eab79..b75aba1 100644 (file)
--- a/lib/librte_eal/include/rte_service_component.h
+++ b/lib/librte_eal/include/rte_service_component.h
@@ -43,7 +43,7 @@ struct rte_service_spec {
 /**
  * Register a new service.
  *
- * A service represents a component that the requires CPU time periodically to
+ * A service represents a component that requires CPU time periodically to
  * achieve its purpose.
  *
  * For example the eventdev SW PMD requires CPU cycles to perform its
@@ -56,6 +56,10 @@ struct rte_service_spec {
  * *rte_service_component_runstate_set*, which indicates that the service
  * component is ready to be executed.
  *
+ * If the service is known to be mapped to a single lcore, setting the
+ * capability of the service to RTE_SERVICE_CAP_MT_SAFE can achieve
+ * better performance.
+ *
  * @param spec The specification of the service to register
  * @param[out] service_id A pointer to a uint32_t, which will be filled in
  *             during registration of the service. It is set to the integers