[ltt-dev] [RFC PATCH 5/7] urcu:implement URCU_BOOST_READER

[Lai Jiangshan]

synchronize_rcu() boosts the reader when it waits for the reader.

Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
---
 urcu.c       |   18 ++++++++++++++++++
 urcu/futex.h |    2 ++
 2 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/urcu.c b/urcu.c
index c13be67..c8164a0 100644
--- a/urcu.c
+++ b/urcu.c
@@ -337,6 +337,13 @@ out:
 }
 #else /* #ifndef URCU_WAIT_READER */
 
+#ifdef URCU_BOOST_READER
+#define urcu_boost_reader() (1)
+#else
+#define urcu_boost_reader() (0)
+#endif
+
+
 static inline void urcu_sync_proxy_lock(int32_t *lock, int32_t proxy_owner)
 {
 	assert(_CMM_LOAD_SHARED(*lock) == 0);
@@ -359,6 +366,12 @@ static void urcu_sync_lock(int32_t *lock, int32_t self)
 				return;
 		}
 
+		if (urcu_boost_reader()) {
+			if (futex_async(lock, FUTEX_LOCK_PI, 0, NULL, NULL, 0) == 0)
+				return;
+			continue;
+		}
+
 		if ((o & FUTEX_WAITERS) == 0) {
 			if (uatomic_cmpxchg(lock, o, o | FUTEX_WAITERS) != o)
 				continue;
@@ -395,6 +408,11 @@ static int urcu_sync_try_unlock(int32_t *lock, int32_t self)
 
 static void urcu_sync_slow_unlock(int32_t *lock)
 {
+	if (urcu_boost_reader()) {
+		futex_async(lock, FUTEX_UNLOCK_PI, 0, NULL, NULL, 0);
+		return;
+	}
+
 	_CMM_STORE_SHARED(*lock, 0);
 	futex_async(lock, FUTEX_WAKE, 1, NULL, NULL, 0);
 }
diff --git a/urcu/futex.h b/urcu/futex.h
index e47c307..cbcd967 100644
--- a/urcu/futex.h
+++ b/urcu/futex.h
@@ -30,6 +30,8 @@ extern "C" {
 
 #define FUTEX_WAIT		0
 #define FUTEX_WAKE		1
+#define FUTEX_LOCK_PI		6
+#define FUTEX_UNLOCK_PI		7
 
 #define FUTEX_WAITERS		0x80000000
 
-- 
1.7.4.4