service: avoid false sharing on core state

For a valid service, the core mask of the service
is checked against the current core and the corresponding
entry in the active_on_lcore array is set or reset.

Upto 8 cores share the same cache line for their
service active_on_lcore array entries since each entry is a uint8_t.
Some number of these entries also share the cache line with
the internal_flags member of struct rte_service_spec_impl,
hence this false sharing also makes the service_valid() check
expensive.

Eliminate false sharing by moving the active_on_lcore array to
a per-core data structure. The array is now indexed by service id.

Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>
Acked-by: Gage Eads <gage.eads@intel.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 fe09077..beb9691 100644 (file)
--- a/lib/librte_eal/common/rte_service.c
+++ b/lib/librte_eal/common/rte_service.c
@@ -51,7 +51,6 @@ struct rte_service_spec_impl {
        rte_atomic32_t num_mapped_cores;
        uint64_t calls;
        uint64_t cycles_spent;
-       uint8_t active_on_lcore[RTE_MAX_LCORE];
 } __rte_cache_aligned;
 
 /* the internal values of a service core */
@@ -60,7 +59,7 @@ struct core_state {
        uint64_t service_mask;
        uint8_t runstate; /* running or stopped */
        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;
        uint64_t calls_per_service[RTE_SERVICE_NUM_MAX];
 } __rte_cache_aligned;
@@ -344,7 +343,7 @@ rte_service_runner_do_callback(struct rte_service_spec_impl *s,
 
 
 static inline int32_t
-service_run(uint32_t i, int lcore, struct core_state *cs, uint64_t service_mask)
+service_run(uint32_t i, struct core_state *cs, uint64_t service_mask)
 {
        if (!service_valid(i))
                return -EINVAL;
@@ -352,11 +351,11 @@ service_run(uint32_t i, int lcore, struct core_state *cs, uint64_t service_mask)
        if (s->comp_runstate != RUNSTATE_RUNNING ||
                        s->app_runstate != RUNSTATE_RUNNING ||
                        !(service_mask & (UINT64_C(1) << i))) {
-               s->active_on_lcore[lcore] = 0;
+               cs->service_active_on_lcore[i] = 0;
                return -ENOEXEC;
        }
 
-       s->active_on_lcore[lcore] = 1;
+       cs->service_active_on_lcore[i] = 1;
 
        /* check do we need cmpset, if MT safe or <= 1 core
         * mapped, atomic ops are not required.
@@ -379,7 +378,6 @@ int32_t
 rte_service_may_be_active(uint32_t id)
 {
        uint32_t ids[RTE_MAX_LCORE] = {0};
-       struct rte_service_spec_impl *s = &rte_services[id];
        int32_t lcore_count = rte_service_lcore_list(ids, RTE_MAX_LCORE);
        int i;
 
@@ -387,7 +385,7 @@ rte_service_may_be_active(uint32_t id)
                return -EINVAL;
 
        for (i = 0; i < lcore_count; i++) {
-               if (s->active_on_lcore[ids[i]])
+               if (lcore_states[i].service_active_on_lcore[id])
                        return 1;
        }
 
@@ -418,7 +416,7 @@ rte_service_run_iter_on_app_lcore(uint32_t id, uint32_t serialize_mt_unsafe)
                return -EBUSY;
        }
 
-       int ret = service_run(id, rte_lcore_id(), cs, UINT64_MAX);
+       int ret = service_run(id, cs, UINT64_MAX);
 
        if (serialize_mt_unsafe)
                rte_atomic32_dec(&s->num_mapped_cores);
@@ -439,7 +437,7 @@ rte_service_runner_func(void *arg)
 
                for (i = 0; i < RTE_SERVICE_NUM_MAX; i++) {
                        /* return value ignored as no change to code flow */
-                       service_run(i, lcore, cs, service_mask);
+                       service_run(i, cs, service_mask);
                }
 
                cs->loops++;