Changeset 99022de in mainline

Timestamp:

2012-11-23T01:23:17Z (11 years ago)

Author:

Adam Hraska <adam.hraska+hos@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

a2f42e5

Parents:

0a597d7

Message:

urcu: Added early exit for rcu_synchronize() if it was stuck waiting for rcu fibril mutex for too long.

File:

• uspace/lib/urcu/rcu.c (modified) (4 diffs)

uspace/lib/urcu/rcu.c

@@ -94 +94 @@
 typedef struct rcu_data {
         fibril_mutex_t mtx;
+        size_t cur_gp;
         size_t reader_group;
         futex_t list_futex;
@@ -106 +107 @@
 static rcu_data_t rcu = {
         .mtx = FIBRIL_MUTEX_INITIALIZER(rcu.mtx),
+        .cur_gp = 0,
         .reader_group = RCU_GROUP_A,
         .list_futex = FUTEX_INITIALIZER,
@@ -183 +185 @@
 void rcu_synchronize(void)
 {
+        /* Contain load of rcu.cur_gp. */
+        memory_barrier();
+
+        /* Approximately the number of the GP in progress. */
+        size_t gp_in_progress = ACCESS_ONCE(rcu.cur_gp);
+        
+        /* todo: early exit for batched sync()s */
+        fibril_mutex_lock(&rcu.mtx);
+        
+        /* 
+         * Exit early if we were stuck waiting for the mutex for a full grace 
+         * period. Started waiting during gp_in_progress (or gp_in_progress + 1
+         * if the value propagated to this cpu too late) so wait for the next
+         * full GP, gp_in_progress + 1, to finish. Ie don't wait if the GP
+         * after that, gp_in_progress + 2, already started.
+         */
+        if (rcu.cur_gp + 2 >= gp_in_progress) {
+                fibril_mutex_unlock(&rcu.mtx);
+                return;
+        }
+        
+        ++ACCESS_ONCE(rcu.cur_gp);
+        
         /* 
          * Pairs up with MB_FORCE_L (ie CC_BAR_L). Makes changes prior 
@@ -188 +213 @@
          */
         memory_barrier(); /* MB_A */
-        
-        /* todo: early exit for batched sync()s */
-        fibril_mutex_lock(&rcu.mtx);
         
         /*