From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Thu, 21 Sep 2023 10:54:18 +0000 (+0100)
Subject: trace.h: Move back nr_callbacks to event description
X-Git-Url: http://git.efficios.com/?p=libside.git;a=commitdiff_plain;h=f8188f94f6e17919ca75063e4d43faca0fd03af8

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 42efeef..f4b1e0f 100644
--- 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 67a5bd4..ec5fdbf 100644
--- 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