Performance: disable event counting by default

Performance improvement changelog from lttng-ust, ported back to
lttng-modules:

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/lib/ringbuffer/backend_internal.h b/lib/ringbuffer/backend_internal.h
index 16001776f6ebcc4b9477c427a868509b9bc5c387..fc5bec535c591b3d9487e555c0dbbbf2055f5dc9 100644 (file)
--- a/lib/ringbuffer/backend_internal.h
+++ b/lib/ringbuffer/backend_internal.h
@@ -201,6 +201,11 @@ int subbuffer_id_check_index(const struct lib_ring_buffer_config *config,
                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 lib_ring_buffer_config *config,
                            struct lib_ring_buffer_backend *bufb,
@@ -211,6 +216,14 @@ void subbuffer_count_record(const struct lib_ring_buffer_config *config,
        sb_bindex = subbuffer_id_get_index(config, bufb->buf_wsb[idx].id);
        v_inc(config, &bufb->array[sb_bindex]->records_commit);
 }
+#else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
+static inline
+void subbuffer_count_record(const struct lib_ring_buffer_config *config,
+                           struct lib_ring_buffer_backend *bufb,
+                           unsigned long idx)
+{
+}
+#endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
 
 /*
  * Reader has exclusive subbuffer access for record consumption. No need to

diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index 6c990c253b483fff101c2b914460458ccf15afcb..9d13d2920420ee6c525d1e22ac0558dc030b7b1f 100644 (file)
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1982,6 +1982,33 @@ void lib_ring_buffer_vmcore_check_deliver(const struct lib_ring_buffer_config *c
                v_set(config, &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 lib_ring_buffer_config *config,
+               struct lib_ring_buffer *buf,
+               unsigned long idx)
+{
+       v_add(config, subbuffer_get_records_count(config,
+                       &buf->backend, idx),
+               &buf->records_count);
+       v_add(config, subbuffer_count_records_overrun(config,
+                       &buf->backend, idx),
+               &buf->records_overrun);
+}
+#else /* LTTNG_RING_BUFFER_COUNT_EVENTS */
+static
+void deliver_count_events(const struct lib_ring_buffer_config *config,
+               struct lib_ring_buffer *buf,
+               unsigned long idx)
+{
+}
+#endif /* #else LTTNG_RING_BUFFER_COUNT_EVENTS */
+
+
 void lib_ring_buffer_check_deliver_slow(const struct lib_ring_buffer_config *config,
                                   struct lib_ring_buffer *buf,
                                   struct channel *chan,
@@ -2034,15 +2061,7 @@ void lib_ring_buffer_check_deliver_slow(const struct lib_ring_buffer_config *con
                 * 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),
-                     &buf->records_count);
-               v_add(config,
-                     subbuffer_count_records_overrun(config,
-                                                     &buf->backend,
-                                                     idx),
-                     &buf->records_overrun);
+               deliver_count_events(config, buf, idx);
                config->cb.buffer_end(buf, tsc, idx,
                                      lib_ring_buffer_get_data_size(config,
                                                                buf,