From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Sun, 25 Sep 2016 15:06:10 +0000 (-0400)
Subject: Performance: Only dereference commit index once
X-Git-Tag: v2.9.0-rc1~12
X-Git-Url: http://git.lttng.org/?p=lttng-modules.git;a=commitdiff_plain;h=8ec496cfb24b29a54c057a332fc91e761994999e

Performance: Only dereference commit index once

The commit fast path should not dereference the commit counter index
repeatedly for performance reasons.

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

diff --git a/lib/ringbuffer/frontend_api.h b/lib/ringbuffer/frontend_api.h
index 517af635..a6f2c6f4 100644
--- a/lib/ringbuffer/frontend_api.h
+++ b/lib/ringbuffer/frontend_api.h
@@ -250,6 +250,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
 	unsigned long offset_end = ctx->buf_offset;
 	unsigned long endidx = subbuf_index(offset_end - 1, chan);
 	unsigned long commit_count;
+	struct commit_counters_hot *cc_hot = &buf->commit_hot[endidx];
 
 	/*
 	 * Must count record before incrementing the commit count.
@@ -270,7 +271,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
 	} else
 		smp_wmb();
 
-	v_add(config, ctx->slot_size, &buf->commit_hot[endidx].cc);
+	v_add(config, ctx->slot_size, &cc_hot->cc);
 
 	/*
 	 * commit count read can race with concurrent OOO commit count updates.
@@ -290,7 +291,7 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
 	 *   count reaches back the reserve offset for a specific sub-buffer,
 	 *   which is completely independent of the order.
 	 */
-	commit_count = v_read(config, &buf->commit_hot[endidx].cc);
+	commit_count = v_read(config, &cc_hot->cc);
 
 	lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
 				      commit_count, endidx, ctx->tsc);
@@ -298,8 +299,8 @@ void lib_ring_buffer_commit(const struct lib_ring_buffer_config *config,
 	 * Update used size at each commit. It's needed only for extracting
 	 * ring_buffer buffers from vmcore, after crash.
 	 */
-	lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
-			offset_end, commit_count);
+	lib_ring_buffer_write_commit_counter(config, buf, chan,
+			offset_end, commit_count, cc_hot);
 }
 
 /**
diff --git a/lib/ringbuffer/frontend_internal.h b/lib/ringbuffer/frontend_internal.h
index a2efee79..88820f7e 100644
--- a/lib/ringbuffer/frontend_internal.h
+++ b/lib/ringbuffer/frontend_internal.h
@@ -288,9 +288,9 @@ static inline
 void lib_ring_buffer_write_commit_counter(const struct lib_ring_buffer_config *config,
 					  struct lib_ring_buffer *buf,
 				          struct channel *chan,
-				          unsigned long idx,
 				          unsigned long buf_offset,
-				          unsigned long commit_count)
+				          unsigned long commit_count,
+					  struct commit_counters_hot *cc_hot)
 {
 	unsigned long commit_seq_old;
 
@@ -306,9 +306,9 @@ void lib_ring_buffer_write_commit_counter(const struct lib_ring_buffer_config *c
 	if (unlikely(subbuf_offset(buf_offset - commit_count, chan)))
 		return;
 
-	commit_seq_old = v_read(config, &buf->commit_hot[idx].seq);
+	commit_seq_old = v_read(config, &cc_hot->seq);
 	if (likely((long) (commit_seq_old - commit_count) < 0))
-		v_set(config, &buf->commit_hot[idx].seq, commit_count);
+		v_set(config, &cc_hot->seq, commit_count);
 }
 
 extern int lib_ring_buffer_create(struct lib_ring_buffer *buf,
diff --git a/lib/ringbuffer/ring_buffer_frontend.c b/lib/ringbuffer/ring_buffer_frontend.c
index 9d13d292..5e691bca 100644
--- a/lib/ringbuffer/ring_buffer_frontend.c
+++ b/lib/ringbuffer/ring_buffer_frontend.c
@@ -1380,9 +1380,9 @@ void lib_ring_buffer_switch_old_start(struct lib_ring_buffer *buf,
 	/* Check if the written buffer has to be delivered */
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->old,
 				      commit_count, oldidx, tsc);
-	lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
+	lib_ring_buffer_write_commit_counter(config, buf, chan,
 			offsets->old + config->cb.subbuffer_header_size(),
-			commit_count);
+			commit_count, &buf->commit_hot[oldidx]);
 }
 
 /*
@@ -1424,8 +1424,9 @@ void lib_ring_buffer_switch_old_end(struct lib_ring_buffer *buf,
 	commit_count = v_read(config, &buf->commit_hot[oldidx].cc);
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->old - 1,
 				      commit_count, oldidx, tsc);
-	lib_ring_buffer_write_commit_counter(config, buf, chan, oldidx,
-			offsets->old + padding_size, commit_count);
+	lib_ring_buffer_write_commit_counter(config, buf, chan,
+			offsets->old + padding_size, commit_count,
+			&buf->commit_hot[oldidx]);
 }
 
 /*
@@ -1466,9 +1467,9 @@ void lib_ring_buffer_switch_new_start(struct lib_ring_buffer *buf,
 	/* Check if the written buffer has to be delivered */
 	lib_ring_buffer_check_deliver(config, buf, chan, offsets->begin,
 				      commit_count, beginidx, tsc);
-	lib_ring_buffer_write_commit_counter(config, buf, chan, beginidx,
+	lib_ring_buffer_write_commit_counter(config, buf, chan,
 			offsets->begin + config->cb.subbuffer_header_size(),
-			commit_count);
+			commit_count, &buf->commit_hot[beginidx]);
 }
 
 /*