cfq: improve fsync performance for small files

Fsync performance for small files achieved by cfq on high-end disks is
lower than what deadline can achieve, due to idling introduced between
the sync write happening in process context and the journal commit.

Moreover, when competing with a sequential reader, a process writing
small files and fsync-ing them is starved.

This patch fixes the two problems by:
- marking journal commits as WRITE_SYNC, so that they get the REQ_NOIDLE
  flag set,
- force all queues that have REQ_NOIDLE requests to be put in the noidle
  tree.

Having the queue associated to the fsync-ing process and the one associated
 to journal commits in the noidle tree allows:
- switching between them without idling,
- fairness vs. competing idling queues, since they will be serviced only
  after the noidle tree expires its slice.

Acked-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Tested-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Corrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

2 files changed, 2 insertions, 2 deletions

diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
index 95d8c11c929..3f030e9efea 100644
--- a/fs/jbd/commit.c
+++ b/fs/jbd/commit.c
@@ -318,7 +318,7 @@ void journal_commit_transaction(journal_t *journal)
 	int first_tag = 0;
 	int tag_flag;
 	int i;
-	int write_op = WRITE;
+	int write_op = WRITE_SYNC;
 
 	/*
 	 * First job: lock down the current transaction and wait for
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 7c068c189d8..80910f51d4b 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -360,7 +360,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	int tag_bytes = journal_tag_bytes(journal);
 	struct buffer_head *cbh = NULL; /* For transactional checksums */
 	__u32 crc32_sum = ~0;
-	int write_op = WRITE;
+	int write_op = WRITE_SYNC;
 
 	/*
 	 * First job: lock down the current transaction and wait for