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authorTejun Heo <tj@kernel.org>2015-08-18 14:55:20 -0700
committerJens Axboe <axboe@fb.com>2015-08-18 15:49:17 -0700
commitae11889636111199dbcf47283b4167f578b69472 (patch)
tree02870926926c7391d41e4b40a8b5bcf82ce34aab /block/blk-throttle.c
parentc9589f03e490956628ff91a1da133216dc796b63 (diff)
blkcg: consolidate blkg creation in blkcg_bio_issue_check()
blkg (blkcg_gq) currently is created by blkcg policies invoking blkg_lookup_create() which ends up repeating about the same code in different policies. Theoretically, this can avoid the overhead of looking and/or creating blkg's if blkcg is enabled but no policy is in use; however, the cost of blkg lookup / creation is very low especially if only the root blkcg is in use which is highly likely if no blkcg policy is in active use - it boils down to a single very predictable conditional and surrounding RCU protection. This patch consolidates blkg creation to a new function blkcg_bio_issue_check() which is called during bio issue from generic_make_request_checks(). blkcg_bio_issue_check() is now the only function which tries to create missing blkg's. The subsequent policy and request_list operations just perform blkg_lookup() and if missing falls back to the root. * blk_get_rl() no longer tries to create blkg. It uses blkg_lookup() instead of blkg_lookup_create(). * blk_throtl_bio() is now called from blkcg_bio_issue_check() with rcu read locked and blkg already looked up. Both throtl_lookup_tg() and throtl_lookup_create_tg() are dropped. * cfq is similarly updated. cfq_lookup_create_cfqg() is replaced with cfq_lookup_cfqg()which uses blkg_lookup(). This consolidates blkg handling and avoids unnecessary blkg creation retries under memory pressure. In addition, this provides a common bio entry point into blkcg where things like common accounting can be performed. v2: Build fixes for !CONFIG_CFQ_GROUP_IOSCHED and !CONFIG_BLK_DEV_THROTTLING. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Arianna Avanzini <avanzini.arianna@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'block/blk-throttle.c')
-rw-r--r--block/blk-throttle.c72
1 files changed, 6 insertions, 66 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 900a777e01c2..29c22ed4b073 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -182,11 +182,6 @@ static inline struct blkcg_gq *tg_to_blkg(struct throtl_grp *tg)
return pd_to_blkg(&tg->pd);
}
-static inline struct throtl_grp *td_root_tg(struct throtl_data *td)
-{
- return blkg_to_tg(td->queue->root_blkg);
-}
-
/**
* sq_to_tg - return the throl_grp the specified service queue belongs to
* @sq: the throtl_service_queue of interest
@@ -449,39 +444,6 @@ static void throtl_pd_reset_stats(struct blkg_policy_data *pd)
}
}
-static struct throtl_grp *throtl_lookup_tg(struct throtl_data *td,
- struct blkcg *blkcg)
-{
- return blkg_to_tg(blkg_lookup(blkcg, td->queue));
-}
-
-static struct throtl_grp *throtl_lookup_create_tg(struct throtl_data *td,
- struct blkcg *blkcg)
-{
- struct request_queue *q = td->queue;
- struct throtl_grp *tg = NULL;
-
- /*
- * This is the common case when there are no blkcgs. Avoid lookup
- * in this case
- */
- if (blkcg == &blkcg_root) {
- tg = td_root_tg(td);
- } else {
- struct blkcg_gq *blkg;
-
- blkg = blkg_lookup_create(blkcg, q);
-
- /* if %NULL and @q is alive, fall back to root_tg */
- if (!IS_ERR(blkg))
- tg = blkg_to_tg(blkg);
- else
- tg = td_root_tg(td);
- }
-
- return tg;
-}
-
static struct throtl_grp *
throtl_rb_first(struct throtl_service_queue *parent_sq)
{
@@ -1403,46 +1365,26 @@ static struct blkcg_policy blkcg_policy_throtl = {
.pd_reset_stats_fn = throtl_pd_reset_stats,
};
-bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
+bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg,
+ struct bio *bio)
{
- struct throtl_data *td = q->td;
struct throtl_qnode *qn = NULL;
- struct throtl_grp *tg;
+ struct throtl_grp *tg = blkg_to_tg(blkg ?: q->root_blkg);
struct throtl_service_queue *sq;
bool rw = bio_data_dir(bio);
- struct blkcg *blkcg;
bool throttled = false;
+ WARN_ON_ONCE(!rcu_read_lock_held());
+
/* see throtl_charge_bio() */
- if (bio->bi_rw & REQ_THROTTLED)
+ if ((bio->bi_rw & REQ_THROTTLED) || !tg->has_rules[rw])
goto out;
- /*
- * A throtl_grp pointer retrieved under rcu can be used to access
- * basic fields like stats and io rates. If a group has no rules,
- * just update the dispatch stats in lockless manner and return.
- */
- rcu_read_lock();
- blkcg = bio_blkcg(bio);
- tg = throtl_lookup_tg(td, blkcg);
- if (tg) {
- if (!tg->has_rules[rw]) {
- throtl_update_dispatch_stats(tg_to_blkg(tg),
- bio->bi_iter.bi_size, bio->bi_rw);
- goto out_unlock_rcu;
- }
- }
-
- /*
- * Either group has not been allocated yet or it is not an unlimited
- * IO group
- */
spin_lock_irq(q->queue_lock);
if (unlikely(blk_queue_bypass(q)))
goto out_unlock;
- tg = throtl_lookup_create_tg(td, blkcg);
sq = &tg->service_queue;
while (true) {
@@ -1507,8 +1449,6 @@ bool blk_throtl_bio(struct request_queue *q, struct bio *bio)
out_unlock:
spin_unlock_irq(q->queue_lock);
-out_unlock_rcu:
- rcu_read_unlock();
out:
/*
* As multiple blk-throtls may stack in the same issue path, we