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

1 files changed, 14 insertions, 13 deletions

diff --git a/kernel/srcu.c b/kernel/srcu.c
index a43211c92863..b9088524935a 100644
--- 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);