From: Pierre Habouzit <madcoder@debian.org>
Date: Thu, 17 Sep 2009 12:30:19 +0000 (-0400)
Subject: qsbr: save two full smp_mb() when the writer is also a reader.
X-Git-Tag: v0.1~80
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=8f50d1ce191ad5f85384c0afbf1ac5b7516ea79f;p=urcu.git

qsbr: save two full smp_mb() when the writer is also a reader.

Now that you've put the barriers before taking lock, and after releasing
it, one can expand the _rcu_thread_{on,off}line call, and optimize two
barrier calls away. (this is patch 1/2).

Signed-off-by: Pierre Habouzit <madcoder@debian.org>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index 4da10d6..3f21be3 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -148,18 +148,18 @@ void synchronize_rcu(void)
 	 * our own quiescent state. This allows using synchronize_rcu() in
 	 * threads registered as readers.
 	 */
+	smp_mb();
 	if (was_online)
-		_rcu_thread_offline();
+		STORE_SHARED(rcu_reader_qs_gp, 0);
 
-	smp_mb();
 	internal_urcu_lock();
 	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + 2);
 	wait_for_quiescent_state();
 	internal_urcu_unlock();
-	smp_mb();
 
 	if (was_online)
-		_rcu_thread_online();
+		_STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr) + 1);
+	smp_mb();
 }
 
 /*