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 a43211c..b908852 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -266,16 +266,16 @@
* 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 @@
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 @@
/*
* 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 @@
* 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 @@
* 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 @@
*/
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 @@
*/
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);