[PATCH 6/8] cfq-iosched: move cfq_group determination from cfq_find_alloc_queue() to cfq_get_queue()

[Tejun Heo]

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 <t...@kernel.org>
Cc: Vivek Goyal <vgo...@redhat.com>
Cc: Arianna Avanzini <avanzini.aria...@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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