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Subject[PATCH 6/8] cfq-iosched: move cfq_group determination from cfq_find_alloc_queue() to cfq_get_queue()
Date
This is necessary for making async cfq_cgroups per-cfq_group instead
of per-cfq_data. While this change makes cfq_get_queue() perform RCU
locking and look up cfq_group even when it reuses async queue, the
extra overhead is extremely unlikely to be noticeable given that this
is already sitting behind cic->cfqq[] cache and the overall cost of
cfq operation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arianna Avanzini <avanzini.arianna@gmail.com>
---
block/cfq-iosched.c | 28 ++++++++++++----------------
1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index b8e83cd..a775128 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -3573,21 +3573,10 @@ static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) {
#endif /* CONFIG_CFQ_GROUP_IOSCHED */

static struct cfq_queue *
-cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
- struct bio *bio)
+cfq_find_alloc_queue(struct cfq_data *cfqd, struct cfq_group *cfqg, bool is_sync,
+ struct cfq_io_cq *cic, struct bio *bio)
{
- struct blkcg *blkcg;
struct cfq_queue *cfqq;
- struct cfq_group *cfqg;
-
- rcu_read_lock();
-
- blkcg = bio_blkcg(bio);
- cfqg = cfq_lookup_create_cfqg(cfqd, blkcg);
- if (!cfqg) {
- cfqq = &cfqd->oom_cfqq;
- goto out;
- }

cfqq = cic_to_cfqq(cic, is_sync);

@@ -3607,8 +3596,6 @@ cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
} else
cfqq = &cfqd->oom_cfqq;
}
-out:
- rcu_read_unlock();
return cfqq;
}

@@ -3638,6 +3625,14 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
int ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
struct cfq_queue **async_cfqq;
struct cfq_queue *cfqq;
+ struct cfq_group *cfqg;
+
+ rcu_read_lock();
+ cfqg = cfq_lookup_create_cfqg(cfqd, bio_blkcg(bio));
+ if (!cfqg) {
+ cfqq = &cfqd->oom_cfqq;
+ goto out;
+ }

if (!is_sync) {
if (!ioprio_valid(cic->ioprio)) {
@@ -3651,7 +3646,7 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
goto out;
}

- cfqq = cfq_find_alloc_queue(cfqd, is_sync, cic, bio);
+ cfqq = cfq_find_alloc_queue(cfqd, cfqg, is_sync, cic, bio);

/*
* pin the queue now that it's allocated, scheduler exit will prune it
@@ -3662,6 +3657,7 @@ cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
}
out:
cfqq->ref++;
+ rcu_read_unlock();
return cfqq;
}

--
2.4.2


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