Commit 66d7e85e authored by Chris Mason's avatar Chris Mason
Browse files

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: default avatarChris Mason <chris.mason@oracle.com>
parent 7f366cfe
......@@ -71,12 +71,13 @@ void btrfs_clear_lock_blocking(struct extent_buffer *eb)
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 @@ int btrfs_try_spin_lock(struct extent_buffer *eb)
/* 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 @@ int btrfs_tree_lock(struct extent_buffer *eb)
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 @@ int btrfs_tree_lock(struct extent_buffer *eb)
* 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);
......
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