blkio: Add io_merged stat

This includes both the number of bios merged into requests belonging to this
cgroup as well as the number of requests merged together.
In the past, we've observed different merging behavior across upstream kernels,
some by design some actual bugs. This stat helps a lot in debugging such
problems when applications report decreased throughput with a new kernel
version.

This needed adding an extra elevator function to capture bios being merged as I
did not want to pollute elevator code with blkiocg knowledge and hence needed
the accounting invocation to come from CFQ.

Signed-off-by: Divyesh Shah<dpshah@google.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 5617ae030b15..4eb1906cf6c6 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1467,6 +1467,14 @@ static void cfq_merged_request(struct request_queue *q, struct request *req,
         }
 }
 
+static void cfq_bio_merged(struct request_queue *q, struct request *req,
+                                struct bio *bio)
+{
+        struct cfq_queue *cfqq = RQ_CFQQ(req);
+        blkiocg_update_io_merged_stats(&cfqq->cfqg->blkg, bio_data_dir(bio),
+                                        cfq_bio_sync(bio));
+}
+
 static void
 cfq_merged_requests(struct request_queue *q, struct request *rq,
                     struct request *next)
@@ -1484,6 +1492,8 @@ cfq_merged_requests(struct request_queue *q, struct request *rq,
         if (cfqq->next_rq == next)
                 cfqq->next_rq = rq;
         cfq_remove_request(next);
+        blkiocg_update_io_merged_stats(&cfqq->cfqg->blkg, rq_data_dir(next),
+                                        rq_is_sync(next));
 }
 
 static int cfq_allow_merge(struct request_queue *q, struct request *rq,
@@ -3861,6 +3871,7 @@ static struct elevator_type iosched_cfq = {
                 .elevator_merged_fn =           cfq_merged_request,
                 .elevator_merge_req_fn =        cfq_merged_requests,
                 .elevator_allow_merge_fn =      cfq_allow_merge,
+                .elevator_bio_merged_fn =       cfq_bio_merged,
                 .elevator_dispatch_fn =         cfq_dispatch_requests,
                 .elevator_add_req_fn =          cfq_insert_request,
                 .elevator_activate_req_fn =     cfq_activate_request,