[Btrfs-devel] [RFS] wait for more writers to join the transaction take 2

[Josef Bacik]

Hello,

Ok so now with this patch we're walloping ext3.  ext3 was getting about 35
files/sec, whereas btrfs was getting 25 files/sec.  With this change btrfs gets
around 170 files/sec.  I yanked out the writer waitqueue as it was causing a
hang b/c we wouldn't wake up.  The only thing thats weird about this, and I
think this is in part because of fs_mutex, is that we _never_ get anybody add
anything to the transaction.  I put debug statements in the do/while loop to
see if we ever loop, and we don't, however we manage to push alot more through
so I'm kind of confused, so if anybody has any ideas I'd love to hear them.
Thanks much,

Josef

diff -r 1765acb6d268 transaction.c
--- a/transaction.c	Tue Aug 07 16:35:25 2007 -0400
+++ b/transaction.c	Wed Aug 08 17:29:58 2007 -0400
@@ -56,8 +56,8 @@ static int join_transaction(struct btrfs
 		root->fs_info->generation++;
 		root->fs_info->running_transaction = cur_trans;
 		cur_trans->num_writers = 0;
+		cur_trans->writers_while_asleep = 0;
 		cur_trans->transid = root->fs_info->generation;
-		init_waitqueue_head(&cur_trans->writer_wait);
 		init_waitqueue_head(&cur_trans->commit_wait);
 		cur_trans->in_commit = 0;
 		cur_trans->use_count = 1;
@@ -67,6 +67,7 @@ static int join_transaction(struct btrfs
 		init_bit_radix(&cur_trans->dirty_pages);
 	}
 	cur_trans->num_writers++;
+	cur_trans->writers_while_asleep++;
 	return 0;
 }
 
@@ -124,8 +125,6 @@ int btrfs_end_transaction(struct btrfs_t
 	WARN_ON(cur_trans != trans->transaction);
 	WARN_ON(cur_trans->num_writers < 1);
 	cur_trans->num_writers--;
-	if (waitqueue_active(&cur_trans->writer_wait))
-		wake_up(&cur_trans->writer_wait);
 	put_transaction(cur_trans);
 	mutex_unlock(&root->fs_info->trans_mutex);
 	memset(trans, 0, sizeof(*trans));
@@ -212,6 +211,7 @@ static int wait_for_commit(struct btrfs_
 			   struct btrfs_transaction *commit)
 {
 	DEFINE_WAIT(wait);
+
 	mutex_lock(&root->fs_info->trans_mutex);
 	while(!commit->commit_done) {
 		prepare_to_wait(&commit->commit_wait, &wait,
@@ -413,12 +413,11 @@ int btrfs_commit_transaction(struct btrf
 int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
 			     struct btrfs_root *root)
 {
-	int ret = 0;
+	int ret = 0, writers = 0;
 	struct btrfs_transaction *cur_trans;
 	struct btrfs_transaction *prev_trans = NULL;
 	struct list_head dirty_fs_roots;
 	struct radix_tree_root pinned_copy;
-	DEFINE_WAIT(wait);
 
 	init_bit_radix(&pinned_copy);
 	INIT_LIST_HEAD(&dirty_fs_roots);
@@ -454,20 +453,19 @@ int btrfs_commit_transaction(struct btrf
 			mutex_lock(&root->fs_info->trans_mutex);
 		}
 	}
-	while (trans->transaction->num_writers > 1) {
+	do{
+		writers = trans->transaction->writers_while_asleep;
 		WARN_ON(cur_trans != trans->transaction);
-		prepare_to_wait(&trans->transaction->writer_wait, &wait,
-				TASK_UNINTERRUPTIBLE);
-		if (trans->transaction->num_writers <= 1)
-			break;
 		mutex_unlock(&root->fs_info->fs_mutex);
 		mutex_unlock(&root->fs_info->trans_mutex);
-		schedule();
+
+		schedule_timeout_uninterruptible(1);
+
 		mutex_lock(&root->fs_info->fs_mutex);
 		mutex_lock(&root->fs_info->trans_mutex);
-		finish_wait(&trans->transaction->writer_wait, &wait);
-	}
-	finish_wait(&trans->transaction->writer_wait, &wait);
+	} while (trans->transaction->num_writers > 1 || 
+		 writers != trans->transaction->writers_while_asleep);
+
 	WARN_ON(cur_trans != trans->transaction);
 	ret = add_dirty_roots(trans, &root->fs_info->fs_roots_radix,
 			      &dirty_fs_roots);
diff -r 1765acb6d268 transaction.h
--- a/transaction.h	Tue Aug 07 16:35:25 2007 -0400
+++ b/transaction.h	Wed Aug 08 17:10:51 2007 -0400
@@ -26,10 +26,10 @@ struct btrfs_transaction {
 	int in_commit;
 	int use_count;
 	int commit_done;
+	unsigned long writers_while_asleep;
 	struct list_head list;
 	struct radix_tree_root dirty_pages;
 	unsigned long start_time;
-	wait_queue_head_t writer_wait;
 	wait_queue_head_t commit_wait;
 };