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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>
This commit is contained in:
Chris Mason 2009-03-12 20:12:45 -04:00
parent 7f366cfecf
commit 66d7e85ea7
1 changed files with 8 additions and 2 deletions
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10
fs/btrfs/locking.c
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@ -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);