rcu: Use single value to handle expedited SRCU grace periods

The earlier algorithm used an "expedited" flag combined with a "trycount"
counter to differentiate between normal and expedited SRCU grace periods.
However, the difference can be encoded into a single counter with a cutoff
value and different initial values for expedited and normal SRCU grace
periods.  This commit makes that change.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Conflicts:

	kernel/srcu.c

diff --git a/kernel/srcu.c b/kernel/srcu.c
index a43211c9286390e52c45efc10bf9d1ceee9ef5b0..b9088524935a07677f25e58e83343b88c3ca8734 100644 (file)
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -266,16 +266,16 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock);
  * we repeatedly block for 1-millisecond time periods.  This approach
  * has done well in testing, so there is no need for a config parameter.
  */
-#define SYNCHRONIZE_SRCU_READER_DELAY 5
+#define SYNCHRONIZE_SRCU_READER_DELAY  5
+#define SYNCHRONIZE_SRCU_TRYCOUNT      2
+#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT  12
 
 /*
  * Wait until all pre-existing readers complete.  Such readers
  * will have used the index specified by "idx".
  */
-static void wait_idx(struct srcu_struct *sp, int idx, bool expedited)
+static void wait_idx(struct srcu_struct *sp, int idx, int trycount)
 {
-       int trycount = 0;
-
        /*
         * SRCU read-side critical sections are normally short, so wait
         * a small amount of time before possibly blocking.
@@ -283,9 +283,10 @@ static void wait_idx(struct srcu_struct *sp, int idx, bool expedited)
        if (!srcu_readers_active_idx_check(sp, idx)) {
                udelay(SYNCHRONIZE_SRCU_READER_DELAY);
                while (!srcu_readers_active_idx_check(sp, idx)) {
-                       if (expedited && ++ trycount < 10)
+                       if (trycount > 0) {
+                               trycount--;
                                udelay(SYNCHRONIZE_SRCU_READER_DELAY);
-                       else
+                       } else
                                schedule_timeout_interruptible(1);
                }
        }
@@ -299,7 +300,7 @@ static void srcu_flip(struct srcu_struct *sp)
 /*
  * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
  */
-static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)
+static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
 {
        int busy_idx;
 
@@ -319,8 +320,8 @@ static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)
         * have completed:
         *
         * __synchronize_srcu() {
-        *      wait_idx(sp, 0, expedited);
-        *      wait_idx(sp, 1, expedited);
+        *      wait_idx(sp, 0, trycount);
+        *      wait_idx(sp, 1, trycount);
         * }
         *
         * Starvation is prevented by the fact that we flip the index.
@@ -344,13 +345,13 @@ static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)
         * this call to wait_idx(), which waits on really old readers
         * describe in this comment above, will almost never need to wait.
         */
-       wait_idx(sp, 1 - busy_idx, expedited);
+       wait_idx(sp, 1 - busy_idx, trycount);
 
        /* Flip the index to avoid reader-induced starvation. */
        srcu_flip(sp);
 
        /* Wait for recent pre-existing readers. */
-       wait_idx(sp, busy_idx, expedited);
+       wait_idx(sp, busy_idx, trycount);
 
        mutex_unlock(&sp->mutex);
 }
@@ -371,7 +372,7 @@ static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)
  */
 void synchronize_srcu(struct srcu_struct *sp)
 {
-       __synchronize_srcu(sp, 0);
+       __synchronize_srcu(sp, SYNCHRONIZE_SRCU_TRYCOUNT);
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu);
 
@@ -392,7 +393,7 @@ EXPORT_SYMBOL_GPL(synchronize_srcu);
  */
 void synchronize_srcu_expedited(struct srcu_struct *sp)
 {
-       __synchronize_srcu(sp, 1);
+       __synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
 }
 EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);