From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Mon, 1 Jul 2013 17:23:11 +0000 (-0400)
Subject: Cleanup: lib_ring_buffer_switch_new_end() only calls subbuffer_set_data_size()
X-Git-Tag: v2.3.0-rc1~15
X-Git-Url: https://git.lttng.org/?p=lttng-modules.git;a=commitdiff_plain;h=768b05c983a930f772079c0085cd5f36f6573b19

Cleanup: lib_ring_buffer_switch_new_end() only calls subbuffer_set_data_size()

lib_ring_buffer_switch_new_end() is always called when an event exactly
fills a sub-buffer, which makes padding_size always 0. However, there is
one side-effect that lib_ring_buffer_switch_new_end() needs to have: it
calls subbuffer_set_data_size() to update the size of the data to be
read from the sub-buffer.

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

diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index 77f9e8bb..077be3c8 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1352,8 +1352,10 @@ void lib_ring_buffer_switch_new_start(struct lib_ring_buffer *buf,
 /*
  * lib_ring_buffer_switch_new_end: finish switching current subbuffer
  *
- * The only remaining threads could be the ones with pending commits. They will
- * have to do the deliver themselves.
+ * Calls subbuffer_set_data_size() to set the data size of the current
+ * sub-buffer. We do not need to perform check_deliver nor commit here,
+ * since this task will be done by the "commit" of the event for which
+ * we are currently doing the space reservation.
  */
 static
 void lib_ring_buffer_switch_new_end(struct lib_ring_buffer *buf,
@@ -1362,33 +1364,11 @@ void lib_ring_buffer_switch_new_end(struct lib_ring_buffer *buf,
 					    u64 tsc)
 {
 	const struct lib_ring_buffer_config *config = &chan->backend.config;
-	unsigned long endidx = subbuf_index(offsets->end - 1, chan);
-	unsigned long commit_count, padding_size, data_size;
+	unsigned long endidx, data_size;
 
+	endidx = subbuf_index(offsets->end - 1, chan);
 	data_size = subbuf_offset(offsets->end - 1, chan) + 1;
-	padding_size = chan->backend.subbuf_size - data_size;
 	subbuffer_set_data_size(config, &buf->backend, endidx, data_size);
-
-	/*
-	 * Order all writes to buffer before the commit count update that will
-	 * determine that the subbuffer is full.
-	 */
-	if (config->ipi == RING_BUFFER_IPI_BARRIER) {
-		/*
-		 * Must write slot data before incrementing commit count.  This
-		 * compiler barrier is upgraded into a smp_mb() by the IPI sent
-		 * by get_subbuf().
-		 */
-		barrier();
-	} else
-		smp_wmb();
-	v_add(config, padding_size, &buf->commit_hot[endidx].cc);
-	commit_count = v_read(config, &buf->commit_hot[endidx].cc);
-	lib_ring_buffer_check_deliver(config, buf, chan, offsets->end - 1,
-				  commit_count, endidx);
-	lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
-					     offsets->end, commit_count,
-					     padding_size);
 }
 
 /*