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Commit 812d4026 authored by Divyesh Shah's avatar Divyesh Shah Committed by Jens Axboe
Browse files

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: default avatarDivyesh <Shah&lt;dpshah@google.com>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 84c124da

Documentation/cgroups/blkio-controller.txt

+5 −0
Original line number Diff line number Diff line
@@ -134,6 +134,11 @@ Details of cgroup files 
	  minor number of the device, third field specifies the operation type

	  and the fourth field specifies the io_wait_time in ns.



- blkio.io_merged

	- Total number of bios/requests merged into requests belonging to this

	  cgroup. This is further divided by the type of operation - read or

	  write, sync or async.



- blkio.dequeue

	- Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y. This

	  gives the statistics about how many a times a group was dequeued

block/blk-cgroup.c

+17 −0
Original line number Diff line number Diff line
@@ -127,6 +127,18 @@ void blkiocg_update_completion_stats(struct blkio_group *blkg, 
}

EXPORT_SYMBOL_GPL(blkiocg_update_completion_stats);



void blkiocg_update_io_merged_stats(struct blkio_group *blkg, bool direction,

					bool sync)

{

	unsigned long flags;



	spin_lock_irqsave(&blkg->stats_lock, flags);

	blkio_add_stat(blkg->stats.stat_arr[BLKIO_STAT_MERGED], 1, direction,

			sync);

	spin_unlock_irqrestore(&blkg->stats_lock, flags);

}

EXPORT_SYMBOL_GPL(blkiocg_update_io_merged_stats);



void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,

			struct blkio_group *blkg, void *key, dev_t dev)

{
@@ -363,6 +375,7 @@ SHOW_FUNCTION_PER_GROUP(io_service_bytes, BLKIO_STAT_SERVICE_BYTES, 1); 
SHOW_FUNCTION_PER_GROUP(io_serviced, BLKIO_STAT_SERVICED, 1);

SHOW_FUNCTION_PER_GROUP(io_service_time, BLKIO_STAT_SERVICE_TIME, 1);

SHOW_FUNCTION_PER_GROUP(io_wait_time, BLKIO_STAT_WAIT_TIME, 1);

SHOW_FUNCTION_PER_GROUP(io_merged, BLKIO_STAT_MERGED, 1);

#ifdef CONFIG_DEBUG_BLK_CGROUP

SHOW_FUNCTION_PER_GROUP(dequeue, BLKIO_STAT_DEQUEUE, 0);

#endif
@@ -407,6 +420,10 @@ struct cftype blkio_files[] = { 
		.name = "io_wait_time",

		.read_map = blkiocg_io_wait_time_read,

	},

	{

		.name = "io_merged",

		.read_map = blkiocg_io_merged_read,

	},

	{

		.name = "reset_stats",

		.write_u64 = blkiocg_reset_stats,

block/blk-cgroup.h

+7 −1
Original line number Diff line number Diff line
@@ -34,6 +34,8 @@ enum stat_type { 
	BLKIO_STAT_SERVICED,

	/* Total time spent waiting in scheduler queue in ns */

	BLKIO_STAT_WAIT_TIME,

	/* Number of IOs merged */

	BLKIO_STAT_MERGED,

	/* All the single valued stats go below this */

	BLKIO_STAT_TIME,

	BLKIO_STAT_SECTORS,
@@ -61,7 +63,7 @@ struct blkio_group_stats { 
	/* total disk time and nr sectors dispatched by this group */

	uint64_t time;

	uint64_t sectors;

	uint64_t stat_arr[BLKIO_STAT_WAIT_TIME + 1][BLKIO_STAT_TOTAL];

	uint64_t stat_arr[BLKIO_STAT_MERGED + 1][BLKIO_STAT_TOTAL];

#ifdef CONFIG_DEBUG_BLK_CGROUP

	/* How many times this group has been removed from service tree */

	unsigned long dequeue;
@@ -148,6 +150,8 @@ void blkiocg_update_dispatch_stats(struct blkio_group *blkg, uint64_t bytes, 
						bool direction, bool sync);

void blkiocg_update_completion_stats(struct blkio_group *blkg,

	uint64_t start_time, uint64_t io_start_time, bool direction, bool sync);

void blkiocg_update_io_merged_stats(struct blkio_group *blkg, bool direction,

					bool sync);

#else

struct cgroup;

static inline struct blkio_cgroup *
@@ -169,5 +173,7 @@ static inline void blkiocg_update_dispatch_stats(struct blkio_group *blkg, 
static inline void blkiocg_update_completion_stats(struct blkio_group *blkg,

		uint64_t start_time, uint64_t io_start_time, bool direction,

		bool sync) {}

static inline void blkiocg_update_io_merged_stats(struct blkio_group *blkg,

						bool direction, bool sync) {}

#endif

#endif /* _BLK_CGROUP_H */

block/blk-core.c

+2 −0
Original line number Diff line number Diff line
@@ -1202,6 +1202,7 @@ static int __make_request(struct request_queue *q, struct bio *bio) 
		if (!blk_rq_cpu_valid(req))

			req->cpu = bio->bi_comp_cpu;

		drive_stat_acct(req, 0);

		elv_bio_merged(q, req, bio);

		if (!attempt_back_merge(q, req))

			elv_merged_request(q, req, el_ret);

		goto out;
@@ -1235,6 +1236,7 @@ static int __make_request(struct request_queue *q, struct bio *bio) 
		if (!blk_rq_cpu_valid(req))

			req->cpu = bio->bi_comp_cpu;

		drive_stat_acct(req, 0);

		elv_bio_merged(q, req, bio);

		if (!attempt_front_merge(q, req))

			elv_merged_request(q, req, el_ret);

		goto out;

block/cfq-iosched.c

+11 −0
Original line number Diff line number Diff line
@@ -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,