Commit f3bdc62f authored by Jan Kara's avatar Jan Kara Committed by Jens Axboe
Browse files

blktrace: Provide event for request merging 



Currently blk-mq does not report any event when two requests get merged
in the elevator. This then results in difficult to understand sequence
of events like:

...
  8,0   34     1579     0.608765271  2718  I  WS 215023504 + 40 [dbench]
  8,0   34     1584     0.609184613  2719  A  WS 215023544 + 56 <- (8,4) 2160568
  8,0   34     1585     0.609184850  2719  Q  WS 215023544 + 56 [dbench]
  8,0   34     1586     0.609188524  2719  G  WS 215023544 + 56 [dbench]
  8,0    3      602     0.609684162   773  D  WS 215023504 + 96 [kworker/3:1H]
  8,0   34     1591     0.609843593     0  C  WS 215023504 + 96 [0]

and you can only guess (after quite some headscratching since the above
excerpt is intermixed with a lot of other IO) that request 215023544+56
got merged to request 215023504+40. Provide proper event for request
merging like we used to do in the legacy block layer.

Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 621c1f42

block/blk-merge.c

+2 −0
Original line number Diff line number Diff line
@@ -793,6 +793,8 @@ static struct request *attempt_merge(struct request_queue *q, 
	 */

	blk_account_io_merge_request(next);



	trace_block_rq_merge(q, next);



	/*

	 * ownership of bio passed from next to req, return 'next' for

	 * the caller to free

include/trace/events/block.h

+15 −0
Original line number Diff line number Diff line
@@ -211,6 +211,21 @@ DEFINE_EVENT(block_rq, block_rq_issue, 
	TP_ARGS(q, rq)

);



/**

 * block_rq_merge - merge request with another one in the elevator

 * @q: queue holding operation

 * @rq: block IO operation operation request

 *

 * Called when block operation request @rq from queue @q is merged to another

 * request queued in the elevator.

 */

DEFINE_EVENT(block_rq, block_rq_merge,



	TP_PROTO(struct request_queue *q, struct request *rq),



	TP_ARGS(q, rq)

);



/**

 * block_bio_bounce - used bounce buffer when processing block operation

 * @q: queue holding the block operation

kernel/trace/blktrace.c

+10 −0
Original line number Diff line number Diff line
@@ -860,6 +860,13 @@ static void blk_add_trace_rq_issue(void *ignore, 
			 blk_trace_request_get_cgid(q, rq));

}



static void blk_add_trace_rq_merge(void *ignore,

				   struct request_queue *q, struct request *rq)

{

	blk_add_trace_rq(rq, 0, blk_rq_bytes(rq), BLK_TA_BACKMERGE,

			 blk_trace_request_get_cgid(q, rq));

}



static void blk_add_trace_rq_requeue(void *ignore,

				     struct request_queue *q,

				     struct request *rq)
@@ -1144,6 +1151,8 @@ static void blk_register_tracepoints(void) 
	WARN_ON(ret);

	ret = register_trace_block_rq_issue(blk_add_trace_rq_issue, NULL);

	WARN_ON(ret);

	ret = register_trace_block_rq_merge(blk_add_trace_rq_merge, NULL);

	WARN_ON(ret);

	ret = register_trace_block_rq_requeue(blk_add_trace_rq_requeue, NULL);

	WARN_ON(ret);

	ret = register_trace_block_rq_complete(blk_add_trace_rq_complete, NULL);
@@ -1190,6 +1199,7 @@ static void blk_unregister_tracepoints(void) 
	unregister_trace_block_bio_bounce(blk_add_trace_bio_bounce, NULL);

	unregister_trace_block_rq_complete(blk_add_trace_rq_complete, NULL);

	unregister_trace_block_rq_requeue(blk_add_trace_rq_requeue, NULL);

	unregister_trace_block_rq_merge(blk_add_trace_rq_merge, NULL);

	unregister_trace_block_rq_issue(blk_add_trace_rq_issue, NULL);

	unregister_trace_block_rq_insert(blk_add_trace_rq_insert, NULL);