urcu: avoid false sharing for rcu_gp_ctr

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index a78c02bdca6a71f9e7f66c76295fc8f1f33cdd37..da6839f0c25b88b4262e9a615bd197220789c185 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -83,16 +83,7 @@ void __attribute__((destructor)) rcu_exit(void);
 #endif
 
 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
-
-int32_t rcu_gp_futex;
-
-/*
- * Global grace period counter.
- * Contains the current RCU_GP_CTR_PHASE.
- * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
- * Written to only by writer with mutex taken. Read by both writer and readers.
- */
-unsigned long rcu_gp_ctr = RCU_GP_COUNT;
+struct urcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
 
 /*
  * Written to only by each individual reader. Read by both the reader and the
@@ -217,8 +208,8 @@ static void wait_gp(void)
 {
        /* Read reader_gp before read futex */
        smp_mb_master(RCU_MB_GROUP);
-       if (uatomic_read(&rcu_gp_futex) == -1)
-               futex_async(&rcu_gp_futex, FUTEX_WAIT, -1,
+       if (uatomic_read(&rcu_gp.futex) == -1)
+               futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
                      NULL, NULL, 0);
 }
 
@@ -232,12 +223,12 @@ static void wait_for_readers(struct cds_list_head *input_readers,
        /*
         * Wait for each thread URCU_TLS(rcu_reader).ctr to either
         * indicate quiescence (not nested), or observe the current
-        * rcu_gp_ctr value.
+        * rcu_gp.ctr value.
         */
        for (;;) {
                wait_loops++;
                if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
-                       uatomic_dec(&rcu_gp_futex);
+                       uatomic_dec(&rcu_gp.futex);
                        /* Write futex before read reader_gp */
                        smp_mb_master(RCU_MB_GROUP);
                }
@@ -270,7 +261,7 @@ static void wait_for_readers(struct cds_list_head *input_readers,
                        if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
                                /* Read reader_gp before write futex */
                                smp_mb_master(RCU_MB_GROUP);
-                               uatomic_set(&rcu_gp_futex, 0);
+                               uatomic_set(&rcu_gp.futex, 0);
                        }
                        break;
                } else {
@@ -289,7 +280,7 @@ static void wait_for_readers(struct cds_list_head *input_readers,
                        if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
                                /* Read reader_gp before write futex */
                                smp_mb_master(RCU_MB_GROUP);
-                               uatomic_set(&rcu_gp_futex, 0);
+                               uatomic_set(&rcu_gp.futex, 0);
                        }
                        break;
                } else {
@@ -357,10 +348,10 @@ void synchronize_rcu(void)
 
        /*
         * Must finish waiting for quiescent state for original parity before
-        * committing next rcu_gp_ctr update to memory. Failure to do so could
+        * committing next rcu_gp.ctr update to memory. Failure to do so could
         * result in the writer waiting forever while new readers are always
         * accessing data (no progress).  Enforce compiler-order of load
-        * URCU_TLS(rcu_reader).ctr before store to rcu_gp_ctr.
+        * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr.
         */
        cmm_barrier();
 
@@ -372,13 +363,13 @@ void synchronize_rcu(void)
        cmm_smp_mb();
 
        /* Switch parity: 0 -> 1, 1 -> 0 */
-       CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
+       CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
 
        /*
-        * Must commit rcu_gp_ctr update to memory before waiting for quiescent
+        * Must commit rcu_gp.ctr update to memory before waiting for quiescent
         * state. Failure to do so could result in the writer waiting forever
         * while new readers are always accessing data (no progress). Enforce
-        * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
+        * compiler-order of store to rcu_gp.ctr before load rcu_reader ctr.
         */
        cmm_barrier();