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From: Corrado Zoccolo on 20 Jul 2010 16:10
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(a)redhat.com>
Reviewed-by: Jeff Moyer <jmoyer(a)redhat.com>
Tested-by: Jeff Moyer <jmoyer(a)redhat.com>
Signed-off-by: Corrado Zoccolo <czoccolo(a)gmail.com>
---
block/cfq-iosched.c | 18 ++++--------------
fs/jbd/commit.c | 2 +-
fs/jbd2/commit.c | 2 +-
3 files changed, 6 insertions(+), 16 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index eb4086f..49dada4 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -216,7 +216,6 @@ struct cfq_data {
enum wl_type_t serving_type;
unsigned long workload_expires;
struct cfq_group *serving_group;
- bool noidle_tree_requires_idle;

/*
* Each priority tree is sorted by next_request position. These
@@ -2126,7 +2125,6 @@ static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
slice = max_t(unsigned, slice, CFQ_MIN_TT);
cfq_log(cfqd, "workload slice:%d", slice);
cfqd->workload_expires = jiffies + slice;
- cfqd->noidle_tree_requires_idle = false;
}

static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
@@ -3108,7 +3106,9 @@ cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
if (cfqq->queued[0] + cfqq->queued[1] >= 4)
cfq_mark_cfqq_deep(cfqq);

- if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle ||
+ if (cfqq->next_rq && (cfqq->next_rq->cmd_flags & REQ_NOIDLE))
+ enable_idle = 0;
+ else if (!atomic_read(&cic->ioc->nr_tasks) || !cfqd->cfq_slice_idle ||
(!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
enable_idle = 0;
else if (sample_valid(cic->ttime_samples)) {
@@ -3421,17 +3421,7 @@ static void cfq_completed_request(struct request_queue *q, struct request *rq)
cfq_slice_expired(cfqd, 1);
else if (sync && cfqq_empty &&
!cfq_close_cooperator(cfqd, cfqq)) {
- cfqd->noidle_tree_requires_idle |=
- !(rq->cmd_flags & REQ_NOIDLE);
- /*
- * Idling is enabled for SYNC_WORKLOAD.
- * SYNC_NOIDLE_WORKLOAD idles at the end of the tree
- * only if we processed at least one !REQ_NOIDLE request
- */
- if (cfqd->serving_type == SYNC_WORKLOAD
- || cfqd->noidle_tree_requires_idle
- || cfqq->cfqg->nr_cfqq == 1)
- cfq_arm_slice_timer(cfqd);
+ cfq_arm_slice_timer(cfqd);
}
}

diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
index 28a9dda..d97a0c6 100644
--- a/fs/jbd/commit.c
+++ b/fs/jbd/commit.c
@@ -317,7 +317,7 @@ 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 75716d3..a078744 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -369,7 +369,7 @@ 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
--
1.6.2.5


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