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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
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+8 −2
Original line number Diff line number Diff line
@@ -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);