Implement sched_yield UP support

[userspace-rcu.git] / urcu-qsbr-static.h

diff --git a/urcu-qsbr-static.h b/urcu-qsbr-static.h
index 87305cb694a9bcc4e175f37829736fcdb81d9686..c39ab817727f4ad6c28c68a4a890b9f7ddcea7a9 100644 (file)
--- a/urcu-qsbr-static.h
+++ b/urcu-qsbr-static.h
@@ -33,8 +33,7 @@
 #include <pthread.h>
 #include <assert.h>
 #include <limits.h>
-#include <syscall.h>
-#include <unistd.h>
+#include <sched.h>
 
 #include <compiler.h>
 #include <arch.h>
@@ -89,10 +88,6 @@
                                (_________p1);                          \
                                })
 
-#define futex(...)             syscall(__NR_futex, __VA_ARGS__)
-#define FUTEX_WAIT             0
-#define FUTEX_WAKE             1
-
 /*
  * This code section can only be included in LGPL 2.1 compatible source code.
  * See below for the function call wrappers which can be used in code meant to
@@ -109,7 +104,7 @@
 #define KICK_READER_LOOPS 10000
 
 /*
- * Active attempts to check for reader Q.S. before calling futex().
+ * Active attempts to check for reader Q.S. before calling sched_yield().
  */
 #define RCU_QS_ACTIVE_ATTEMPTS 100
 
@@ -173,7 +168,8 @@ static inline void reader_barrier()
 }
 
 #define RCU_GP_ONLINE          (1UL << 0)
-#define RCU_GP_CTR             (1UL << 1)
+#define RCU_GP_ONGOING         (1UL << 1)
+#define RCU_GP_CTR             (1UL << 2)
 
 /*
  * Global quiescent period counter with low-order bits unused.
@@ -184,20 +180,6 @@ extern unsigned long urcu_gp_ctr;
 
 extern unsigned long __thread rcu_reader_qs_gp;
 
-extern int gp_futex;
-
-/*
- * Wake-up waiting synchronize_rcu(). Called from many concurrent threads.
- */
-static inline void wake_up_gp(void)
-{
-       if (unlikely(atomic_read(&gp_futex) == -1)) {
-               atomic_set(&gp_futex, 0);
-               futex(&gp_futex, FUTEX_WAKE, 1,
-                     NULL, NULL, 0);
-       }
-}
-
 #if (BITS_PER_LONG < 64)
 static inline int rcu_gp_ongoing(unsigned long *value)
 {
@@ -231,10 +213,15 @@ static inline void _rcu_read_unlock(void)
 
 static inline void _rcu_quiescent_state(void)
 {
-       smp_mb();       
-       _STORE_SHARED(rcu_reader_qs_gp, _LOAD_SHARED(urcu_gp_ctr));
-       smp_mb();       /* write rcu_reader_qs_gp before read futex */
-       wake_up_gp();
+       long gp_ctr;
+
+       smp_mb();
+       gp_ctr = LOAD_SHARED(urcu_gp_ctr);
+       if (unlikely(gp_ctr & RCU_GP_ONGOING)) {
+               sched_yield();
+               gp_ctr = LOAD_SHARED(urcu_gp_ctr);
+       }
+       _STORE_SHARED(rcu_reader_qs_gp, gp_ctr);
        smp_mb();
 }
 
@@ -242,13 +229,18 @@ static inline void _rcu_thread_offline(void)
 {
        smp_mb();
        STORE_SHARED(rcu_reader_qs_gp, 0);
-       smp_mb();       /* write rcu_reader_qs_gp before read futex */
-       wake_up_gp();
 }
 
 static inline void _rcu_thread_online(void)
 {
-       _STORE_SHARED(rcu_reader_qs_gp, LOAD_SHARED(urcu_gp_ctr));
+       long gp_ctr;
+
+       gp_ctr = LOAD_SHARED(urcu_gp_ctr);
+       if (unlikely(gp_ctr & RCU_GP_ONGOING)) {
+               sched_yield();
+               gp_ctr = LOAD_SHARED(urcu_gp_ctr);
+       }
+       _STORE_SHARED(rcu_reader_qs_gp, gp_ctr);
        smp_mb();
 }