[PATCH 6/7] blkcg: account requests instead of bios for request based request_queues

[Tejun Heo]

blkcg accounting is currently bio based, which is silly for request
based request_queues.  This is silly as the number of bios doesn't
have much to do with the actual number of IOs issued to the underlying
device (can be significantly higher or lower) and may change depending
on the implementation details on how the bios are issued (e.g. from
the recent split-bios-while-issuing change).

request based request_queues have QUEUE_FLAG_IO_STAT set by default
which controls the gendisk accounting.  Do cgroup accounting for those
request_queues together with gendisk accounting on request completion.

This makes cgroup accounting consistent with gendisk accounting and
what's happening on the system.

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
---
 block/blk-core.c           |  3 +++
 include/linux/blk-cgroup.h | 18 +++++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 048be4a..ad23b96 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -2429,6 +2429,7 @@ void blk_account_io_completion(struct request *req, unsigned int bytes)
 		cpu = part_stat_lock();
 		part = req->part;
 		part_stat_add(cpu, part, sectors[rw], bytes >> 9);
+		blkcg_account_io_completion(req, bytes);
 		part_stat_unlock();
 	}
 }
@@ -2454,6 +2455,8 @@ void blk_account_io_done(struct request *req)
 		part_round_stats(req->q, cpu, part);
 		part_dec_in_flight(req->q, part, rw);
 
+		blkcg_account_io_done(req);
+
 		hd_struct_put(part);
 		part_stat_unlock();
 	}
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 96eed0f..f2f9691 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -715,7 +715,8 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
 
 	throtl = blk_throtl_bio(q, blkg, bio);
 
-	if (!throtl) {
+	/* if @q does io stat, blkcg stats are updated together with them */
+	if (!blk_queue_io_stat(q) && !throtl) {
 		blkg_rwstat_add(&blkg->stat_bytes, bio->bi_opf,
 				bio->bi_iter.bi_size);
 		blkg_rwstat_add(&blkg->stat_ios, bio->bi_opf, 1);
@@ -764,6 +765,17 @@ static inline void blk_rq_disassociate_blkg(struct request *rq)
 	rq->blkg = NULL;
 }
 
+static inline void blkcg_account_io_completion(struct request *rq,
+					       unsigned int bytes)
+{
+	blkg_rwstat_add(&rq->blkg->stat_bytes, rq_data_dir(rq), bytes);
+}
+
+static inline void blkcg_account_io_done(struct request *rq)
+{
+	blkg_rwstat_add(&rq->blkg->stat_ios, rq_data_dir(rq), 1);
+}
+
 #else	/* CONFIG_BLK_CGROUP */
 
 struct blkcg {
@@ -823,6 +835,10 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
 static inline void blk_rq_associate_blkg(struct request *rq, struct blkcg *blkcg) { }
 static inline void blk_rq_disassociate_blkg(struct request *rq) { }
 
+static inline void blkcg_account_io_completion(struct request *rq,
+					       unsigned int bytes) { }
+static inline void blkcg_account_io_done(struct request *rq) { }
+
 #define blk_queue_for_each_rl(rl, q)	\
 	for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)
 
-- 
2.9.5