From 66d7e85ea7c3628189d19b265495358f756cb463 Mon Sep 17 00:00:00 2001
From: Chris Mason <chris.mason@oracle.com>
Date: Thu, 12 Mar 2009 20:12:45 -0400
Subject: 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>
---
fs/btrfs/locking.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
(limited to 'fs/btrfs')
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 47b0a88c12a2..6d8db2f5c38d 100644
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -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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