trace.h: Move back nr_callbacks to event description

nr_callbacks is not used on the fast path, therefore move it back to the
event description to optimize cache density of the event state enabled
flags.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/include/side/trace.h b/include/side/trace.h
index 42efeefda9803ca5a474a89ba576b736c268767f..f4b1e0ff66c679385f1f9ed8625b2dc625c2b5dc 100644 (file)
--- a/include/side/trace.h
+++ b/include/side/trace.h
@@ -658,7 +658,6 @@ struct side_tracer_dynamic_struct_visitor_ctx {
 struct side_event_state {
        uintptr_t enabled;
        const struct side_callback *callbacks;
-       uint32_t nr_callbacks;
 };
 
 struct side_event_description {
@@ -672,6 +671,7 @@ struct side_event_description {
        side_enum_t(enum side_loglevel, uint32_t) loglevel;
        uint32_t nr_fields;
        uint32_t nr_attr;
+       uint32_t nr_callbacks;
 } SIDE_PACKED;
 
 /* Event and type attributes */
@@ -1808,7 +1808,6 @@ struct side_event_description {
                        side_event_state__##_identifier = { \
                .enabled = 0, \
                .callbacks = &side_empty_callback, \
-               .nr_callbacks = 0, \
        }; \
        _linkage struct side_event_description __attribute__((section("side_event_description"))) \
                        _identifier = { \
@@ -1822,6 +1821,7 @@ struct side_event_description {
                .loglevel = SIDE_ENUM_INIT(_loglevel), \
                .nr_fields = SIDE_ARRAY_SIZE(SIDE_PARAM(_fields)), \
                .nr_attr = SIDE_ARRAY_SIZE(SIDE_PARAM_SELECT_ARG1(_, ##_attr, side_attr_list())), \
+               .nr_callbacks = 0, \
        }; \
        static const struct side_event_description *side_event_ptr__##_identifier \
                __attribute__((section("side_event_description_ptr"), used)) = &(_identifier);

diff --git a/src/side.c b/src/side.c
index 67a5bd459a15734e40287c72d57dc57d6a65c91b..ec5fdbf81b367de829522435f1509a02e5c0b74b 100644 (file)
--- a/src/side.c
+++ b/src/side.c
@@ -148,7 +148,7 @@ int _side_tracer_callback_register(struct side_event_description *desc,
                side_init();
        pthread_mutex_lock(&side_lock);
        event_state = side_ptr_get(desc->state);
-       old_nr_cb = event_state->nr_callbacks;
+       old_nr_cb = desc->nr_callbacks;
        if (old_nr_cb == UINT32_MAX) {
                ret = SIDE_ERROR_INVAL;
                goto unlock;
@@ -177,7 +177,7 @@ int _side_tracer_callback_register(struct side_event_description *desc,
        side_rcu_wait_grace_period(&rcu_gp);
        if (old_nr_cb)
                free(old_cb);
-       event_state->nr_callbacks++;
+       desc->nr_callbacks++;
        /* Increment concurrently with kernel setting the top bits. */
        if (!old_nr_cb)
                (void) __atomic_add_fetch(&event_state->enabled, 1, __ATOMIC_RELAXED);
@@ -227,7 +227,7 @@ static int _side_tracer_callback_unregister(struct side_event_description *desc,
                ret = SIDE_ERROR_NOENT;
                goto unlock;
        }
-       old_nr_cb = event_state->nr_callbacks;
+       old_nr_cb = desc->nr_callbacks;
        old_cb = (struct side_callback *) event_state->callbacks;
        if (old_nr_cb == 1) {
                new_cb = (struct side_callback *) &side_empty_callback;
@@ -246,7 +246,7 @@ static int _side_tracer_callback_unregister(struct side_event_description *desc,
        side_rcu_assign_pointer(event_state->callbacks, new_cb);
        side_rcu_wait_grace_period(&rcu_gp);
        free(old_cb);
-       event_state->nr_callbacks--;
+       desc->nr_callbacks--;
        /* Decrement concurrently with kernel setting the top bits. */
        if (old_nr_cb == 1)
                (void) __atomic_add_fetch(&event_state->enabled, -1, __ATOMIC_RELAXED);
@@ -304,7 +304,7 @@ static
 void side_event_remove_callbacks(struct side_event_description *desc)
 {
        struct side_event_state *event_state = side_ptr_get(desc->state);
-       uint32_t nr_cb = event_state->nr_callbacks;
+       uint32_t nr_cb = desc->nr_callbacks;
        struct side_callback *old_cb;
 
        if (!nr_cb)
@@ -316,7 +316,7 @@ void side_event_remove_callbacks(struct side_event_description *desc)
         * caution. This should not matter because instrumentation is
         * unreachable.
         */
-       event_state->nr_callbacks = 0;
+       desc->nr_callbacks = 0;
        side_rcu_assign_pointer(event_state->callbacks, &side_empty_callback);
        /*
         * No need to wait for grace period because instrumentation is