From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Fri, 9 Sep 2016 20:54:20 +0000 (-0400)
Subject: Performance: disable event counting by default
X-Git-Tag: v2.9.0-rc1~19
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=9c995331b51a9b9a8c85457a897fa89e770de111;p=lttng-ust.git

Performance: disable event counting by default

Disable event counting in the ring buffer, which can count the number of
events produced per ring-buffer, as well as the number of events
overwritten in overwrite mode.

This feature is currently unused anyway: it is not saved in the ring
buffer header, nor made available to lttng-tools.

This saves 70 ns/event in lttng-ust on the ARM32 Cubietruck.

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

diff --git a/libringbuffer/backend_internal.h b/libringbuffer/backend_internal.h
index df3617ca..7bd5c738 100644
--- a/libringbuffer/backend_internal.h
+++ b/libringbuffer/backend_internal.h
@@ -196,6 +196,11 @@ int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config *conf
 		return 0;
 }
 
+/*
+ * The ring buffer can count events recorded and overwritten per buffer,
+ * but it is disabled by default due to its performance overhead.
+ */
+#ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
 static inline
 void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config *config,
 			    struct lttng_ust_lib_ring_buffer_backend *bufb,
@@ -206,6 +211,14 @@ void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config *confi
 	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
 	v_inc(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit);
 }
+#else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
+static inline
+void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config *config,
+			    struct lttng_ust_lib_ring_buffer_backend *bufb,
+			    unsigned long idx, struct lttng_ust_shm_handle *handle)
+{
+}
+#endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
 
 /*
  * Reader has exclusive subbuffer access for record consumption. No need to
diff --git a/libringbuffer/ring_buffer_frontend.c b/libringbuffer/ring_buffer_frontend.c
index 14ae8eb3..1396f44a 100644
--- a/libringbuffer/ring_buffer_frontend.c
+++ b/libringbuffer/ring_buffer_frontend.c
@@ -2168,6 +2168,34 @@ void lib_ring_buffer_vmcore_check_deliver(const struct lttng_ust_lib_ring_buffer
 		v_set(config, &shmp_index(handle, buf->commit_hot, idx)->seq, commit_count);
 }
 
+/*
+ * The ring buffer can count events recorded and overwritten per buffer,
+ * but it is disabled by default due to its performance overhead.
+ */
+#ifdef LTTNG_RING_BUFFER_COUNT_EVENTS
+static
+void deliver_count_events(const struct lttng_ust_lib_ring_buffer_config *config,
+		struct lttng_ust_lib_ring_buffer *buf,
+		unsigned long idx,
+		struct lttng_ust_shm_handle *handle)
+{
+	v_add(config, subbuffer_get_records_count(config,
+			&buf->backend, idx, handle),
+		&buf->records_count);
+	v_add(config, subbuffer_count_records_overrun(config,
+			&buf->backend, idx, handle),
+		&buf->records_overrun);
+}
+#else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
+static
+void deliver_count_events(const struct lttng_ust_lib_ring_buffer_config *config,
+		struct lttng_ust_lib_ring_buffer *buf,
+		unsigned long idx,
+		struct lttng_ust_shm_handle *handle)
+{
+}
+#endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
+
 void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_config *config,
 				   struct lttng_ust_lib_ring_buffer *buf,
 			           struct channel *chan,
@@ -2221,16 +2249,7 @@ void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_c
 		 * and any other writer trying to access this subbuffer
 		 * in this state is required to drop records.
 		 */
-		v_add(config,
-		      subbuffer_get_records_count(config,
-						  &buf->backend,
-						  idx, handle),
-		      &buf->records_count);
-		v_add(config,
-		      subbuffer_count_records_overrun(config,
-						      &buf->backend,
-						      idx, handle),
-		      &buf->records_overrun);
+		deliver_count_events(config, buf, idx, handle);
 		config->cb.buffer_end(buf, tsc, idx,
 				      lib_ring_buffer_get_data_size(config,
 								buf,