Btrfs: Check for a blocking lock before taking the spin
This reduces contention on the extent buffer spin locks by testing for a
blocking lock before trying to take the spinlock.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 47b0a88..6d8db2f 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -71,12 +71,13 @@
static int btrfs_spin_on_block(struct extent_buffer *eb)
{
int i;
+
for (i = 0; i < 512; i++) {
- cpu_relax();
if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags))
return 1;
if (need_resched())
break;
+ cpu_relax();
}
return 0;
}
@@ -102,6 +103,7 @@
/* spin for a bit on the BLOCKING flag */
for (i = 0; i < 2; i++) {
+ cpu_relax();
if (!btrfs_spin_on_block(eb))
break;
@@ -148,6 +150,9 @@
DEFINE_WAIT(wait);
wait.func = btrfs_wake_function;
+ if (!btrfs_spin_on_block(eb))
+ goto sleep;
+
while(1) {
spin_nested(eb);
@@ -165,9 +170,10 @@
* spin for a bit, and if the blocking flag goes away,
* loop around
*/
+ cpu_relax();
if (btrfs_spin_on_block(eb))
continue;
-
+sleep:
prepare_to_wait_exclusive(&eb->lock_wq, &wait,
TASK_UNINTERRUPTIBLE);