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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

fs/btrfs/locking.c

+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);